Add format_string routine to format other types to strings

doc/specs/stdlib_ascii.md

@@ -212,42 +212,4 @@ program demo_reverse
     implicit none
     print'(a)', reverse("Hello, World!") ! returns "!dlroW ,olleH"
 end program demo_reverse
-```
-
-### `to_string`
-
-#### Status
-
-Experimental
-
-#### Description
-
-Create a character string representing the value of the provided variable.
-
-#### Syntax
-
-`res = [[stdlib_ascii(module):to_string(interface)]] (string)`
-
-#### Class
-
-Pure function.
-
-#### Argument
-
-`val`: shall be an intrinsic integer or logical type. It is an `intent(in)` argument.
-
-#### Result value
-
-The result is an intrinsic character type.
-
-#### Example
-
-```fortran
-program demo_string_value
-    use stdlib_ascii, only : to_string
-    implicit none
-    print'(a)', to_string(-3) ! returns "-3"
-    print'(a)', to_string(.true.) ! returns "T"
-    print'(a)', to_string(42) ! returns "42"
-end program demo_string_value
-```
+```

doc/specs/stdlib_strings.md

@@ -538,3 +538,72 @@ program demo_count
 
 end program demo_count
 ```
+
+<!-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -->
+### `to_string`
+
+#### Description
+
+Format or transfer a `integer/real/complex/logical` scalar as a string.  
+Input a wrong `format` that cause the internal-IO to fail, the result value is a string of `[*]`.
+
+#### Syntax
+
+`string = [[stdlib_strings(module):to_string(interface)]] (value [, format])`
+
+#### Status
+
+Experimental
+
+#### Class
+
+Pure function.
+
+#### Argument
+
+- `value`: Shall be an `integer/real/complex/logical` scalar.
+  This is an `intent(in)` argument.
+- `format`: Shall be a `character(len=*)` scalar like `'(F6.2)'` or just `'F6.2'`.
+  This is an `intent(in)` and `optional` argument.  
+  Contains the edit descriptor to format `value` into a string, for example `'(F6.2)'` or `'(f6.2)'`. 
+  `to_string` will automatically enclose `format` in a set of parentheses, so passing `F6.2` or `f6.2` as `format` is possible as well.
+
+#### Result value
+
+The result is an `allocatable` length `character` scalar with up to `128` cached `character` length.
+
+#### Example
+
+```fortran
+program demo_to_string
+    use stdlib_strings, only: to_string
+
+    !> Example for `complex` type
+    print *, to_string((1, 1))              !! "(1.00000000,1.00000000)"
+    print *, to_string((1, 1), '(F6.2)')    !! "(  1.00,  1.00)"
+    print *, to_string((1000, 1), '(ES0.2)'), to_string((1000, 1), '(SP,F6.3)')     
+                    !! "(1.00E+3,1.00)""(******,+1.000)"
+                    !! Too narrow formatter for real number
+                    !! Normal demonstration(`******` from Fortran Standard)
+
+    !> Example for `integer` type
+    print *, to_string(-3)                  !! "-3"
+    print *, to_string(42, '(I4)')          !! "  42"
+    print *, to_string(1, '(I0.4)'), to_string(2, '(B4)')           !! "0001""  10"  
+
+    !> Example for `real` type
+    print *, to_string(1.)                  !! "1.00000000"
+    print *, to_string(1., '(F6.2)')        !! "  1.00" 
+    print *, to_string(1., 'F6.2')          !! "  1.00" 
+    print *, to_string(1., '(SP,ES9.2)'), to_string(1, '(F7.3)')    !! "+1.00E+00""[*]"
+                    !! 1 wrong demonstration (`[*]` from `to_string`)
+
+    !> Example for `logical` type
+    print *, to_string(.true.)              !! "T"
+    print *, to_string(.true., '(L2)')      !! " T"
+    print *, to_string(.true., 'L2')        !! " T"
+    print *, to_string(.false., '(I5)')     !! "[*]"
+                    !! 1 wrong demonstrations(`[*]` from `to_string`)
+
+end program demo_to_string
+```

src/CMakeLists.txt

@@ -34,6 +34,9 @@ set(fppFiles
     stdlib_math_logspace.fypp
     stdlib_math_arange.fypp
     stdlib_string_type.fypp
+    stdlib_string_type_constructor.fypp
+    stdlib_strings_to_string.fypp
+    stdlib_strings.fypp
 )
 
 
@@ -52,7 +55,6 @@ set(SRC
     stdlib_error.f90
     stdlib_kinds.f90
     stdlib_logger.f90
-    stdlib_strings.f90
     stdlib_system.F90
     stdlib_specialfunctions.f90
     stdlib_specialfunctions_legendre.f90

src/Makefile.manual

@@ -1,4 +1,4 @@
-SRCFYPP =\
+SRCFYPP = \
         stdlib_ascii.fypp \
         stdlib_bitsets_64.fypp \
         stdlib_bitsets_large.fypp \
@@ -27,10 +27,13 @@ SRCFYPP =\
         stdlib_stats_moment_scalar.fypp \
         stdlib_stats_var.fypp \
         stdlib_math.fypp \
-		stdlib_math_linspace.fypp \
-		stdlib_math_logspace.fypp \
+	stdlib_math_linspace.fypp \
+	stdlib_math_logspace.fypp \
         stdlib_stats_distribution_PRNG.fypp \
-        stdlib_string_type.fypp
+        stdlib_string_type.fypp \
+        stdlib_string_type_constructor.fypp \
+        stdlib_strings.fypp \
+        stdlib_strings_to_string.fypp
 
 SRC = f18estop.f90 \
       stdlib_error.f90 \
@@ -40,7 +43,6 @@ SRC = f18estop.f90 \
       stdlib_kinds.f90 \
       stdlib_logger.f90 \
       stdlib_quadrature_gauss.f90 \
-      stdlib_strings.f90 \
       $(SRCGEN)
 
 LIB = libstdlib.a
@@ -77,85 +79,89 @@ stdlib_error.o: stdlib_optval.o
 stdlib_specialfunctions.o: stdlib_kinds.o
 stdlib_specialfunctions_legendre.o: stdlib_kinds.o stdlib_specialfunctions.o
 stdlib_io.o: \
-	stdlib_ascii.o \
-	stdlib_error.o \
-	stdlib_optval.o \
-	stdlib_kinds.o
+    stdlib_ascii.o \
+    stdlib_error.o \
+    stdlib_optval.o \
+    stdlib_kinds.o \
+    stdlib_ascii.o
 stdlib_linalg.o: \
-	stdlib_kinds.o
+    stdlib_kinds.o
 stdlib_linalg_diag.o: \
-	stdlib_linalg.o \
-	stdlib_kinds.o
+    stdlib_linalg.o \
+    stdlib_kinds.o
 stdlib_logger.o: stdlib_ascii.o stdlib_optval.o
 stdlib_optval.o: stdlib_kinds.o
 stdlib_quadrature.o: stdlib_kinds.o
-
 stdlib_quadrature_gauss.o: stdlib_kinds.o stdlib_quadrature.o
-
 stdlib_quadrature_simps.o: \
-	stdlib_quadrature.o \
-	stdlib_error.o \
-	stdlib_kinds.o
+    stdlib_quadrature.o \
+    stdlib_error.o \
+    stdlib_kinds.o
 stdlib_quadrature_trapz.o: \
-	stdlib_quadrature.o \
-	stdlib_error.o \
-	stdlib_kinds.o
+    stdlib_quadrature.o \
+    stdlib_error.o \
+    stdlib_kinds.o
 stdlib_sorting.o: \
-	stdlib_kinds.o \
-	stdlib_string_type.o
+    stdlib_kinds.o \
+    stdlib_string_type.o
 stdlib_sorting_ord_sort.o: \
-	stdlib_sorting.o
+    stdlib_sorting.o
 stdlib_sorting_sort.o: \
-	stdlib_sorting.o
+    stdlib_sorting.o
 stdlib_sorting_sort_index.o: \
-	stdlib_sorting.o
+    stdlib_sorting.o
 stdlib_stats.o: \
-	stdlib_kinds.o
+    stdlib_kinds.o
 stdlib_stats_corr.o: \
-	stdlib_optval.o \
-	stdlib_kinds.o \
-	stdlib_stats.o
+    stdlib_optval.o \
+    stdlib_kinds.o \
+    stdlib_stats.o
 stdlib_stats_cov.o: \
-	stdlib_optval.o \
-	stdlib_kinds.o \
-	stdlib_stats.o
+    stdlib_optval.o \
+    stdlib_kinds.o \
+    stdlib_stats.o
 stdlib_stats_mean.o: \
-	stdlib_optval.o \
-	stdlib_kinds.o \
-	stdlib_stats.o
+    stdlib_optval.o \
+    stdlib_kinds.o \
+    stdlib_stats.o
 stdlib_stats_median.o: \
-	stdlib_optval.o \
-	stdlib_kinds.o \
-	stdlib_sorting.o \
-	stdlib_stats.o
+    stdlib_optval.o \
+    stdlib_kinds.o \
+    stdlib_sorting.o \
+    stdlib_stats.o
 stdlib_stats_moment.o: \
-	stdlib_optval.o \
-	stdlib_kinds.o \
-	stdlib_stats.o
+    stdlib_optval.o \
+    stdlib_kinds.o \
+    stdlib_stats.o
 stdlib_stats_moment_all.o: \
-	stdlib_stats_moment.o
+    stdlib_stats_moment.o
 stdlib_stats_moment_mask.o: \
-	stdlib_stats_moment.o
+    stdlib_stats_moment.o
 stdlib_stats_moment_scalar.o: \
-	stdlib_stats_moment.o
+    stdlib_stats_moment.o
 stdlib_stats_var.o: \
-	stdlib_optval.o \
-	stdlib_kinds.o \
-	stdlib_stats.o
+    stdlib_optval.o \
+    stdlib_kinds.o \
+    stdlib_stats.o
 stdlib_stats_distribution_PRNG.o: \
-        stdlib_kinds.o \
-	stdlib_error.o
+    stdlib_kinds.o \
+    stdlib_error.o
 stdlib_string_type.o: stdlib_ascii.o \
     stdlib_kinds.o
+stdlib_string_type_constructor.o: stdlib_string_type.o \
+    stdlib_strings_to_string.o \
+    stdlib_strings.o
 stdlib_strings.o: stdlib_ascii.o \
     stdlib_string_type.o \
-	stdlib_optval.o
+    stdlib_optval.o \
+    stdlib_kinds.o
+stdlib_strings_to_string.o: stdlib_strings.o
 stdlib_math.o: stdlib_kinds.o \
     stdlib_optval.o
 stdlib_math_linspace.o: \
-	stdlib_math.o
+    stdlib_math.o
 stdlib_math_logspace.o: \
-	stdlib_math_linspace.o
+    stdlib_math_linspace.o
 stdlib_math_arange.o: \
     stdlib_math.o
 stdlib_linalg_outer_product.o: stdlib_linalg.o

src/stdlib_ascii.fypp

@@ -20,19 +20,6 @@ module stdlib_ascii
 
     ! Character conversion functions
     public :: to_lower, to_upper, to_title, to_sentence, reverse
-    public :: to_string
-
-    !> Version: experimental
-    !>
-    !> Create a character string representing the value of the provided variable.
-    interface to_string
-    #:for kind in INT_KINDS
-        module procedure :: to_string_integer_${kind}$
-    #:endfor
-    #:for kind in LOG_KINDS
-        module procedure :: to_string_logical_${kind}$
-    #:endfor
-    end interface to_string
 
     ! All control characters in the ASCII table (see www.asciitable.com).
     character(len=1), public, parameter :: NUL = achar(int(z'00')) !! Null
@@ -362,51 +349,4 @@ contains
 
     end function reverse
 
-    #:for kind in INT_KINDS
-    !> Represent an integer of kind ${kind}$ as character sequence
-    pure function to_string_integer_${kind}$(val) result(string)
-        integer, parameter :: ik = ${kind}$
-        integer(ik), intent(in) :: val
-        character(len=:), allocatable :: string
-        integer, parameter :: buffer_len = range(val)+2
-        character(len=buffer_len) :: buffer
-        integer :: pos
-        integer(ik) :: n
-        character(len=1), parameter :: numbers(0:9) = &
-            ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]
-
-        if (val == 0_ik) then
-            string = numbers(0)
-            return
-        end if
-
-        n = abs(val)
-        buffer = ""
-
-        pos = buffer_len + 1
-        do while (n > 0_ik)
-            pos = pos - 1
-            buffer(pos:pos) = numbers(mod(n, 10_ik))
-            n = n/10_ik
-        end do
-        if (val < 0_ik) then
-            pos = pos - 1
-            buffer(pos:pos) = '-'
-        end if
-
-        string = buffer(pos:)
-    end function to_string_integer_${kind}$
-    #:endfor
-
-    #:for kind in LOG_KINDS
-    !> Represent an logical of kind ${kind}$ as character sequence
-    pure function to_string_logical_${kind}$(val) result(string)
-        integer, parameter :: ik = ${kind}$
-        logical(ik), intent(in) :: val
-        character(len=1) :: string
-
-        string = merge("T", "F", val)
-    end function to_string_logical_${kind}$
-    #:endfor
-
 end module stdlib_ascii

src/stdlib_string_type.fypp

@@ -14,7 +14,7 @@
 !> The specification of this module is available [here](../page/specs/stdlib_string_type.html).
 module stdlib_string_type
     use stdlib_ascii, only: to_lower_ => to_lower, to_upper_ => to_upper, &
-       & to_title_ => to_title, to_sentence_ => to_sentence, reverse_ => reverse, to_string
+       & to_title_ => to_title, to_sentence_ => to_sentence, reverse_ => reverse
     use stdlib_kinds, only : int8, int16, int32, int64, lk, c_bool
     implicit none
     private
@@ -42,25 +42,33 @@ module stdlib_string_type
         character(len=:), allocatable :: raw
     end type string_type
 
-    !> Constructor for new string instances
-    interface string_type
-        module procedure :: new_string
-      #:for kind in INT_KINDS
-        module procedure :: new_string_from_integer_${kind}$
-      #:endfor
-      #:for kind in LOG_KINDS
-        module procedure :: new_string_from_logical_${kind}$
-      #:endfor
-    end interface string_type
-
-
     !> Returns the length of the character sequence represented by the string.
     !>
     !> This method is elemental and returns a default integer scalar value.
     interface len
         module procedure :: len_string
     end interface len
 
+    !> Constructor for new string instances
+    interface string_type
+        pure elemental module function new_string(string) result(new)
+            character(len=*), intent(in), optional :: string
+            type(string_type) :: new
+        end function new_string
+        #:for kind in INT_KINDS
+        pure elemental module function new_string_from_integer_${kind}$(val) result(new)
+            integer(${kind}$), intent(in) :: val
+            type(string_type) :: new
+        end function new_string_from_integer_${kind}$
+        #:endfor
+        #:for kind in LOG_KINDS
+        pure elemental module function new_string_from_logical_${kind}$(val) result(new)
+            logical(${kind}$), intent(in) :: val
+            type(string_type) :: new
+        end function new_string_from_logical_${kind}$
+        #:endfor
+    end interface string_type        
+
     !> Returns the length of the character sequence without trailing spaces
     !> represented by the string.
     !>
@@ -356,35 +364,6 @@ module stdlib_string_type
 
 contains
 
-
-    !> Constructor for new string instances from a scalar character value.
-    elemental function new_string(string) result(new)
-        character(len=*), intent(in), optional :: string
-        type(string_type) :: new
-        if (present(string)) then
-            new%raw = string
-        end if
-    end function new_string
-
-  #:for kind in INT_KINDS
-    !> Constructor for new string instances from an integer of kind ${kind}$.
-    elemental function new_string_from_integer_${kind}$(val) result(new)
-        integer(${kind}$), intent(in) :: val
-        type(string_type) :: new
-        new%raw = to_string(val)
-    end function new_string_from_integer_${kind}$
-  #:endfor
-
-  #:for kind in LOG_KINDS
-    !> Constructor for new string instances from a logical of kind ${kind}$.
-    elemental function new_string_from_logical_${kind}$(val) result(new)
-        logical(${kind}$), intent(in) :: val
-        type(string_type) :: new
-        new%raw = to_string(val)
-    end function new_string_from_logical_${kind}$
-  #:endfor
-
-
     !> Assign a character sequence to a string.
     elemental subroutine assign_string_char(lhs, rhs)
         type(string_type), intent(inout) :: lhs

src/stdlib_string_type_constructor.fypp

@@ -0,0 +1,35 @@
+#:include "common.fypp"
+submodule(stdlib_string_type) stdlib_string_type_constructor
+
+    use stdlib_strings, only: to_string
+
+contains
+
+    !> Constructor for new string instances from a scalar character value.
+    elemental module function new_string(string) result(new)
+        character(len=*), intent(in), optional :: string
+        type(string_type) :: new
+        if (present(string)) then
+            new%raw = string
+        end if
+    end function new_string
+
+    #:for kind in INT_KINDS
+    !> Constructor for new string instances from an integer of kind ${kind}$.
+    elemental module function new_string_from_integer_${kind}$(val) result(new)
+        integer(${kind}$), intent(in) :: val
+        type(string_type) :: new
+        new%raw = to_string(val)
+    end function new_string_from_integer_${kind}$
+    #:endfor
+
+    #:for kind in LOG_KINDS
+    !> Constructor for new string instances from a logical of kind ${kind}$.
+    elemental module function new_string_from_logical_${kind}$(val) result(new)
+        logical(${kind}$), intent(in) :: val
+        type(string_type) :: new
+        new%raw = to_string(val)
+    end function new_string_from_logical_${kind}$
+    #:endfor
+
+end submodule stdlib_string_type_constructor

src/stdlib_strings.f90 → src/stdlib_strings.fypp

@@ -1,19 +1,47 @@
 ! SPDX-Identifier: MIT
-
+#:include "common.fypp"
 !> This module implements basic string handling routines.
 !>
 !> The specification of this module is available [here](../page/specs/stdlib_strings.html).
 module stdlib_strings
     use stdlib_ascii, only: whitespace
     use stdlib_string_type, only: string_type, char, verify, repeat, len
     use stdlib_optval, only: optval
+    use stdlib_kinds, only: sp, dp, qp, int8, int16, int32, int64, lk, c_bool
     implicit none
     private
 
+    public :: to_string
     public :: strip, chomp
     public :: starts_with, ends_with
     public :: slice, find, replace_all, padl, padr, count
 
+    !> Version: experimental
+    !>
+    !> Format or transfer other types as a string.
+    !> ([Specification](../page/specs/stdlib_strings.html#to_string))
+    interface to_string
+        #:set RC_KINDS_TYPES = REAL_KINDS_TYPES + CMPLX_KINDS_TYPES
+        #:set IL_KINDS_TYPES = INT_KINDS_TYPES + LOG_KINDS_TYPES
+        #:for k1, t1 in RC_KINDS_TYPES
+        pure module function to_string_${t1[0]}$_${k1}$(value, format) result(string)
+            ${t1}$, intent(in) :: value
+            character(len=*), intent(in), optional :: format
+            character(len=:), allocatable :: string
+        end function to_string_${t1[0]}$_${k1}$
+        #:endfor
+        #:for k1, t1 in IL_KINDS_TYPES
+        pure module function to_string_1_${t1[0]}$_${k1}$(value) result(string)
+            ${t1}$, intent(in) :: value
+            character(len=#{if t1[0]=="l"}#1)#{else}#:), allocatable#{endif}# :: string 
+        end function to_string_1_${t1[0]}$_${k1}$
+        pure module function to_string_2_${t1[0]}$_${k1}$(value, format) result(string)
+            ${t1}$, intent(in) :: value
+            character(len=*), intent(in) :: format
+            character(len=:), allocatable :: string
+        end function to_string_2_${t1[0]}$_${k1}$
+        #:endfor
+    end interface to_string
 
     !> Remove leading and trailing whitespace characters.
     !>

src/stdlib_strings_to_string.fypp

@@ -0,0 +1,123 @@
+#:include "common.fypp"
+submodule(stdlib_strings) stdlib_strings_to_string
+
+    integer, parameter :: buffer_len = 128
+    character(len=*), parameter :: err_sym = "[*]"
+        !!TODO: [*]?
+
+contains
+
+    #:for k1, t1 in REAL_KINDS_TYPES
+    !> Format or transfer a ${t1}$ scalar as a string.
+    pure module function to_string_${t1[0]}$_${k1}$(value, format) result(string)
+        ${t1}$, intent(in) :: value
+        character(len=*), intent(in), optional :: format
+        character(len=:), allocatable :: string
+
+        character(len=buffer_len) :: buffer
+        integer :: stat
+
+        write(buffer, '(' // optval(format, "g0") // ')', iostat=stat) value
+        if (stat == 0) then
+            string = trim(buffer)
+        else
+            string = err_sym
+        end if
+
+    end function to_string_${t1[0]}$_${k1}$
+    #:endfor
+
+    #:for k1, t1 in CMPLX_KINDS_TYPES
+    !> Format or transfer a ${t1}$ scalar as a string.
+    pure module function to_string_${t1[0]}$_${k1}$(value, format) result(string)
+        ${t1}$, intent(in) :: value
+        character(len=*), intent(in), optional :: format
+        character(len=:), allocatable :: string
+
+        string = '(' // to_string_r_${k1}$(value%re, format) // ',' // &
+                      & to_string_r_${k1}$(value%im, format) // ')'
+
+    end function to_string_${t1[0]}$_${k1}$
+    #:endfor
+
+    #:for k1, t1 in INT_KINDS_TYPES
+    !> Represent an integer of kind ${k1}$ as character sequence.
+    pure module function to_string_1_${t1[0]}$_${k1}$(value) result(string)
+        ${t1}$, intent(in) :: value
+        character(len=:), allocatable :: string
+        integer, parameter :: buffer_len = range(value)+2
+        character(len=buffer_len) :: buffer
+        integer :: pos
+        ${t1}$ :: n
+        character(len=1), parameter :: numbers(0:9) = &
+            ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]
+
+        if (value == 0_${k1}$) then
+            string = numbers(0)
+            return
+        end if
+
+        n = abs(value)
+        buffer = ""
+
+        pos = buffer_len + 1
+        do while (n > 0_${k1}$)
+            pos = pos - 1
+            buffer(pos:pos) = numbers(mod(n, 10_${k1}$))
+            n = n/10_${k1}$
+        end do
+        if (value < 0_${k1}$) then
+            pos = pos - 1
+            buffer(pos:pos) = '-'
+        end if
+
+        string = buffer(pos:)
+    end function to_string_1_${t1[0]}$_${k1}$
+
+    pure module function to_string_2_${t1[0]}$_${k1}$(value, format) result(string)
+        ${t1}$, intent(in) :: value
+        character(len=*), intent(in) :: format
+        character(len=:), allocatable :: string
+
+        character(len=buffer_len) :: buffer
+        integer :: stat
+
+        write(buffer, "(" // format // ")", iostat=stat) value
+        if (stat == 0) then
+            string = trim(buffer)
+        else
+            string = err_sym
+        end if
+
+    end function to_string_2_${t1[0]}$_${k1}$
+    #:endfor
+
+    #:for k1, t1 in LOG_KINDS_TYPES
+    !> Represent an logical of kind ${k1}$ as character sequence.
+    pure module function to_string_1_${t1[0]}$_${k1}$(value) result(string)
+        ${t1}$, intent(in) :: value
+        character(len=1) :: string
+
+        string = merge("T", "F", value)
+
+    end function to_string_1_${t1[0]}$_${k1}$
+
+    pure module function to_string_2_${t1[0]}$_${k1}$(value, format) result(string)
+        ${t1}$, intent(in) :: value
+        character(len=*), intent(in) :: format
+        character(len=:), allocatable :: string
+
+        character(len=buffer_len) :: buffer
+        integer :: stat
+
+        write(buffer, "(" // format // ")", iostat=stat) value
+        if (stat == 0) then
+            string = trim(buffer)
+        else
+            string = err_sym
+        end if
+
+    end function to_string_2_${t1[0]}$_${k1}$
+    #:endfor
+
+end submodule stdlib_strings_to_string

src/tests/ascii/test_ascii.f90

@@ -6,8 +6,7 @@ program test_ascii
         whitespace, letters, is_alphanum, is_alpha, is_lower, is_upper, &
         is_digit, is_octal_digit, is_hex_digit, is_white, is_blank, &
         is_control, is_punctuation, is_graphical, is_printable, is_ascii, &
-        to_lower, to_upper, to_title, to_sentence, reverse, LF, TAB, NUL, DEL, &
-        to_string
+        to_lower, to_upper, to_title, to_sentence, reverse, LF, TAB, NUL, DEL
     use stdlib_kinds, only : int8, int16, int32, int64, lk, c_bool
 
     implicit none
@@ -76,8 +75,6 @@ program test_ascii
     call test_to_sentence_string
     call test_reverse_string
 
-    call test_to_string
-
 contains
 
     subroutine test_is_alphanum_short
@@ -640,47 +637,4 @@ subroutine test_reverse_string
         call check(trim(adjustl(dlc)) == "desrever")
     end subroutine test_reverse_string
 
-    subroutine test_to_string
-       character(len=128) :: flc
-
-       write(flc, '(g0)') 1026192
-       call check(to_string(1026192) == trim(flc))
-
-       write(flc, '(g0)') -124784
-       call check(to_string(-124784) == trim(flc))
-
-       write(flc, '(g0)') 1_int8
-       call check(to_string(1_int8) == trim(flc))
-
-       write(flc, '(g0)') -3_int8
-       call check(to_string(-3_int8) == trim(flc))
-
-       write(flc, '(g0)') 80_int16
-       call check(to_string(80_int16) == trim(flc))
-
-       write(flc, '(g0)') 8924890_int32
-       call check(to_string(8924890_int32) == trim(flc))
-
-       write(flc, '(g0)') -2378401_int32
-       call check(to_string(-2378401_int32) == trim(flc))
-
-       write(flc, '(g0)') -921092378401_int64
-       call check(to_string(-921092378401_int64) == trim(flc))
-
-       write(flc, '(g0)') 1272835771_int64
-       call check(to_string(1272835771_int64) == trim(flc))
-
-       write(flc, '(g0)') .true.
-       call check(to_string(.true.) == trim(flc))
-
-       write(flc, '(g0)') .false.
-       call check(to_string(.false.) == trim(flc))
-
-       write(flc, '(g0)') .true._c_bool
-       call check(to_string(.true._c_bool) == trim(flc))
-
-       write(flc, '(g0)') .false._lk
-       call check(to_string(.false._lk) == trim(flc))
-    end subroutine test_to_string
-
 end program test_ascii

src/tests/string/CMakeLists.txt

@@ -5,3 +5,4 @@ ADDTEST(string_match)
 ADDTEST(string_derivedtype_io)
 ADDTEST(string_functions)
 ADDTEST(string_strip_chomp)
+ADDTEST(string_to_string)

src/tests/string/Makefile.manual

@@ -4,7 +4,8 @@ PROGS_SRC = test_string_assignment.f90 \
             test_string_intrinsic.f90 \
             test_string_match.f90 \
             test_string_operator.f90 \
-            test_string_strip_chomp.f90
+            test_string_strip_chomp.f90 \
+            test_string_to_string.f90
 
 
 include ../Makefile.manual.test.mk

src/tests/string/test_string_functions.f90

@@ -6,7 +6,7 @@ module test_string_functions
                                     to_lower, to_upper, to_title, to_sentence, reverse
     use stdlib_strings, only: slice, find, replace_all, padl, padr, count
     use stdlib_optval, only: optval
-    use stdlib_ascii, only : to_string
+    use stdlib_strings, only : to_string
     implicit none
 
 contains

src/tests/string/test_string_to_string.f90

@@ -0,0 +1,113 @@
+! SPDX-Identifier: MIT
+module test_string_to_string
+
+    use stdlib_strings, only: to_string, starts_with
+    use stdlib_error, only: check
+    use stdlib_optval, only: optval
+    implicit none
+
+contains
+
+    subroutine check_formatter(actual, expected, description, partial)
+        character(len=*), intent(in) :: actual, expected, description
+        logical, intent(in), optional :: partial
+        logical :: stat
+        character(len=:), allocatable :: msg
+
+        if (optval(partial, .false.)) then
+            stat = starts_with(actual, expected)
+        else
+            stat = actual == expected
+        end if
+
+        if (.not. stat) then
+            msg = description // new_line("a") // &
+                & "Expected: '" // expected // "' but got '" // actual // "'"
+        else
+            print '(" - ", a, /, "   Result: ''", a, "''")', description, actual
+        end if
+
+        call check(stat, msg)
+
+    end subroutine check_formatter
+
+    subroutine test_to_string_complex
+        call check_formatter(to_string((1, 1)), "(1.0", &
+                & "Default formatter for complex number", partial=.true.)
+        call check_formatter(to_string((1, 1), '(F6.2)'), "(  1.00,  1.00)", &
+                & "Formatter for complex number")
+        call check_formatter(to_string((-1, -1), 'F6.2'), "( -1.00, -1.00)", &
+                & "Formatter for negative complex number")
+        call check_formatter(to_string((1, 1), 'SP,F6.2'), "( +1.00, +1.00)", &
+                & "Formatter with sign control descriptor for complex number")
+        call check_formatter(to_string((1, 1), 'F6.2') // to_string((2, 2), '(F7.3)'), &
+                & "(  1.00,  1.00)(  2.000,  2.000)", &
+                & "Multiple formatters for complex numbers")
+
+    end subroutine test_to_string_complex
+
+    subroutine test_to_string_integer
+        call check_formatter(to_string(100), "100", &
+                & "Default formatter for integer number")
+        call check_formatter(to_string(100, 'I6'), "   100", &
+                & "Formatter for integer number")
+        call check_formatter(to_string(100, 'I0.6'), "000100", &
+                & "Formatter with zero padding for integer number")
+        call check_formatter(to_string(100, 'I6') // to_string(1000, '(I7)'), &
+                & "   100   1000", "Multiple formatters for integers")
+        call check_formatter(to_string(34, 'B8'), "  100010", &
+                & "Binary formatter for integer number")
+        call check_formatter(to_string(34, 'O0.3'), "042", &
+                & "Octal formatter with zero padding for integer number")
+        call check_formatter(to_string(34, 'Z3'), " 22", &
+                & "Hexadecimal formatter for integer number")
+
+    end subroutine test_to_string_integer
+
+    subroutine test_to_string_real
+        call check_formatter(to_string(100.), "100.0", &
+                & "Default formatter for real number", partial=.true.)
+        call check_formatter(to_string(100., 'F6.2'), "100.00", &
+                & "Formatter for real number")
+        call check_formatter(to_string(289., 'E7.2'), ".29E+03", &
+                & "Exponential formatter with rounding for real number")
+        call check_formatter(to_string(128., 'ES8.2'), "1.28E+02", &
+                & "Exponential formatter for real number")
+
+      ! Wrong demonstration
+        call check_formatter(to_string(-100., 'F6.2'), "*", &
+                & "Too narrow formatter for signed real number", partial=.true.)
+        call check_formatter(to_string(1000., 'F6.3'), "*", &
+                & "Too narrow formatter for real number", partial=.true.)
+        call check_formatter(to_string(1000., '7.3'), "[*]", &
+                & "Invalid formatter for real number", partial=.true.)
+
+    end subroutine test_to_string_real
+
+    subroutine test_to_string_logical
+        call check_formatter(to_string(.true.), "T", &
+                & "Default formatter for logcal value")
+        call check_formatter(to_string(.true., 'L2'), " T", &
+                & "Formatter for logical value")
+        call check_formatter(to_string(.false., 'L2') // to_string(.true., '(L5)'), &
+                & " F    T", "Multiple formatters for logical values")
+
+      ! Wrong demonstration
+        call check_formatter(to_string(.false., '1x'), "[*]", &
+                & "Invalid formatter for logical value", partial=.true.)
+
+    end subroutine test_to_string_logical
+
+
+end module test_string_to_string
+
+program tester
+    use test_string_to_string
+    implicit none
+
+    call test_to_string_complex
+    call test_to_string_integer
+    call test_to_string_logical
+    call test_to_string_real
+
+end program tester