add example

Author: perazz

doc/specs/stdlib_strings.md

@@ -547,8 +547,8 @@ The result is an `allocatable` length `character` scalar with up to `128` cached
 
 #### Description
 
-Convert a Fortran character string to a C character array.  
-This function converts a Fortran string into a C-style string, ensuring proper null-termination for use in C functions or libraries.  
+Convert a Fortran `character` string or a `type(string_type)` variable to a C character array.  
+This function converts a Fortran string into a C-style array of characters, ensuring proper null-termination for use in C functions or libraries.  
 
 #### Syntax
 
@@ -564,8 +564,7 @@ Pure function.
 
 #### Argument
 
-- `value`: Shall be a `character(len=*)` string.  
-  This is an `intent(in)` argument.  
+- `value`: Shall be a `character(len=*)` string or a `type(string_type)` variable. It is an `intent(in)` argument.  
   The Fortran string that will be converted to a C character array.
 
 #### Result value

example/strings/CMakeLists.txt

@@ -9,6 +9,7 @@ ADD_EXAMPLE(slice)
 ADD_EXAMPLE(starts_with)
 ADD_EXAMPLE(strip)
 ADD_EXAMPLE(to_string)
+ADD_EXAMPLE(to_c_string)
 ADD_EXAMPLE(zfill)
 ADD_EXAMPLE(string_to_number)
-ADD_EXAMPLE(stream_of_strings_to_numbers)
+ADD_EXAMPLE(stream_of_strings_to_numbers)

example/strings/example_to_c_string.f90

@@ -0,0 +1,22 @@
+program example_to_c_string
+  use stdlib_strings, only: to_c_string
+  use stdlib_string_type, only: string_type
+  use stdlib_kinds, only: c_char
+  implicit none
+  
+  character(kind=c_char), allocatable :: cstr(:),cstr2(:)
+  character(*), parameter :: hello = "Hello, World!"
+  
+  ! Convert character array
+  cstr = to_c_string(hello)
+  
+  ! Convert string type  
+  cstr2 = to_c_string(string_type(hello))
+    
+  if (size(cstr)==size(cstr2) .and. all(cstr==cstr2)) then 
+     stop 0
+  else
+     error stop 'String conversion error'
+  end if
+  
+end program example_to_c_string