Improve to_string: add support for format like 'f6.2'.

Author: zoziha

doc/specs/stdlib_strings.md

@@ -563,9 +563,11 @@ Pure function.
 
 - `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)'`.
-  This is an `intent(in)` and `optional` 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.
@@ -575,7 +577,6 @@ The result is an `allocatable` length `character` scalar with up to `128` cached
 ```fortran
 program demo_to_string
     use stdlib_strings, only: to_string
-    implicit none
 
     !> Example for `complex` type
     print *, to_string((1, 1))              !! "(1.00000000,1.00000000)"
@@ -593,14 +594,16 @@ program demo_to_string
     !> 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'), to_string(.false., '(I5)')    !! "[*]""[*]"
-                    !! 2 wrong demonstrations(`[*]` from `to_string`)
+    print *, to_string(.true., 'L2')        !! " T"
+    print *, to_string(.false., '(I5)')     !! "[*]"
+                    !! 1 wrong demonstrations(`[*]` from `to_string`)
 
 end program demo_to_string
 ```

src/stdlib_strings_to_string.fypp

@@ -17,7 +17,7 @@ contains
         character(len=buffer_len) :: buffer
         integer :: stat
 
-        write(buffer, optval(format, "(g0)"), iostat=stat) value
+        write(buffer, '(' // optval(format, "g0") // ')', iostat=stat) value
         if (stat == 0) then
             string = trim(buffer)
         else
@@ -82,7 +82,7 @@ contains
         character(len=buffer_len) :: buffer
         integer :: stat
 
-        write(buffer, format, iostat=stat) value
+        write(buffer, "(" // format // ")", iostat=stat) value
         if (stat == 0) then
             string = trim(buffer)
         else
@@ -110,7 +110,7 @@ contains
         character(len=buffer_len) :: buffer
         integer :: stat
 
-        write(buffer, format, iostat=stat) value
+        write(buffer, "(" // format // ")", iostat=stat) value
         if (stat == 0) then
             string = trim(buffer)
         else

src/tests/string/test_string_to_string.f90

@@ -36,11 +36,11 @@ subroutine test_to_string_complex
                 & "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)", &
+        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)", &
+        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)'), &
+        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")
 
@@ -49,51 +49,51 @@ 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", &
+        call check_formatter(to_string(100, 'I6'), "   100", &
                 & "Formatter for integer number")
-        call check_formatter(to_string(100, '(I0.6)'), "000100", &
+        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)'), &
+        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", &
+        call check_formatter(to_string(34, 'B8'), "  100010", &
                 & "Binary formatter for integer number")
-        call check_formatter(to_string(34, '(O0.3)'), "042", &
+        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", &
+        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", &
+        call check_formatter(to_string(100., 'F6.2'), "100.00", &
                 & "Formatter for real number")
-        call check_formatter(to_string(289., '(E7.2)'), ".29E+03", &
+        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", &
+        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)'), "*", &
+        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)'), "*", &
+        call check_formatter(to_string(1000., 'F6.3'), "*", &
                 & "Too narrow formatter for real number", partial=.true.)
-        call check_formatter(to_string(1000., '(7.3)'), "[*]", &
+        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", &
+        call check_formatter(to_string(.true., 'L2'), " T", &
                 & "Formatter for logical value")
-        call check_formatter(to_string(.false., '(L2)') // to_string(.true., '(L5)'), &
+        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)'), "[*]", &
+        call check_formatter(to_string(.false., '1x'), "[*]", &
                 & "Invalid formatter for logical value", partial=.true.)
 
     end subroutine test_to_string_logical