strings: join, to_c_char

doc/specs/stdlib_strings.md

@@ -459,6 +459,43 @@ The result is of the same type as `string`.
 {!example/strings/example_zfill.f90!}
 ```
 
+<!-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -->
+### `join`
+
+#### Description
+
+Joins an array of strings into a single string. This function concatenates the strings from the input array, 
+inserting a separator between each string (default: space). A user-defined separator may be provided, The resulting string is returned.
+
+
+#### Syntax
+
+`cmd = ` [[stdlib_strings(module):join(interface)]] ` (strings, separator)`
+
+#### Status
+
+Experimental
+
+#### Class
+
+Pure function
+
+#### Argument
+
+- `strings`: Array of strings (either `type(string_type)` or `character(len=*)`).
+  This argument is `intent(in)`. It is an array of strings that will be concatenated together.
+- `separator`: `character(len=*)` scalar (optional).
+  This argument is `intent(in)`. It specifies the separator to be used between the strings. If not provided, the default separator (a space) is used.
+
+#### Result value
+
+The result is of the same type as the elements of `strings` (`type(string_type)` or `character(len=:), allocatable`).
+
+#### Example
+
+```fortran
+{!example/strings/example_join.f90!}
+```
 
 <!-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -->
 ### `to_string`
@@ -498,3 +535,38 @@ The result is an `allocatable` length `character` scalar with up to `128` cached
 ```fortran
 {!example/strings/example_to_string.f90!}
 ```
+
+<!-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -->
+### `to_c_string`
+
+#### Description
+
+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
+
+`cstr = ` [[stdlib_strings(module):to_c_string(function)]] ` (value)`
+
+#### Status
+
+Experimental
+
+#### Class
+
+Pure function.
+
+#### 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
+
+The result is a `character(kind=c_char)` array with a dimension of `len(value) + 1` to accommodate the null terminator.
+
+#### Example
+
+```fortran
+{!example/strings/example_to_c_string.f90!}
+```

example/strings/CMakeLists.txt

@@ -2,13 +2,15 @@ ADD_EXAMPLE(chomp)
 ADD_EXAMPLE(count)
 ADD_EXAMPLE(ends_with)
 ADD_EXAMPLE(find)
+ADD_EXAMPLE(join)
 ADD_EXAMPLE(padl)
 ADD_EXAMPLE(padr)
 ADD_EXAMPLE(replace_all)
 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_join.f90

@@ -0,0 +1,21 @@
+program example_join
+  use stdlib_strings, only: join
+  implicit none
+
+  character(len=:), allocatable :: line
+  character(*), parameter :: words(3) = [character(7) :: "Hello", "World", "Fortran"]
+
+  ! Default separator (space)
+  line = join(words)
+  print *, "'" // line // "'"   !! 'Hello World Fortran'
+
+  ! Custom separator
+  line = join(words, "_")
+  print *, "'" // line // "'"  !! 'Hello_World_Fortran'
+
+  ! Custom 2-character separator
+  line = join(words, ", ")
+  print *, "'" // line // "'"  !! 'Hello, World, Fortran'
+
+  stop 0
+end program example_join

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

src/stdlib_kinds.fypp

@@ -4,10 +4,10 @@
 !> The specification of this module is available [here](../page/specs/stdlib_kinds.html).
 module stdlib_kinds
   use iso_fortran_env, only: int8, int16, int32, int64
-  use iso_c_binding, only: c_bool
+  use iso_c_binding, only: c_bool, c_char
   implicit none
   private
-  public :: sp, dp, xdp, qp, int8, int16, int32, int64, lk, c_bool
+  public :: sp, dp, xdp, qp, int8, int16, int32, int64, lk, c_bool, c_char
 
   !> Single precision real numbers
   integer, parameter :: sp = selected_real_kind(6)

src/stdlib_strings.fypp

@@ -5,16 +5,18 @@
 !> 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_string_type, only: string_type, char, verify, repeat, len, len_trim, move
     use stdlib_optval, only: optval
-    use stdlib_kinds, only: sp, dp, xdp, qp, int8, int16, int32, int64, lk, c_bool
+    use stdlib_kinds, only: sp, dp, xdp, qp, int8, int16, int32, int64, lk, c_bool, c_char
+    use iso_c_binding, only: c_null_char
     implicit none
     private
 
     public :: to_string
+    public :: to_c_string
     public :: strip, chomp
     public :: starts_with, ends_with
-    public :: slice, find, replace_all, padl, padr, count, zfill
+    public :: slice, find, replace_all, padl, padr, count, zfill, join
 
     !> Version: experimental
     !>
@@ -43,6 +45,15 @@ module stdlib_strings
         #:endfor
     end interface to_string
 
+    !> Version: experimental
+    !>
+    !> Format or transfer other types as a string.
+    !> ([Specification](../page/specs/stdlib_strings.html#to_c_string))
+    interface to_c_string
+        module procedure to_c_string_from_char
+        module procedure to_c_string_from_string
+    end interface to_c_string
+
     !> Remove leading and trailing whitespace characters.
     !>
     !> Version: experimental
@@ -164,6 +175,17 @@ module stdlib_strings
         module procedure :: zfill_char
     end interface zfill
 
+    !> Version: experimental
+    !>
+    !> Joins an array of strings into a single string. 
+    !> The chunks are separated with a space, or an optional user-defined separator.
+    !> [Specifications](../page/specs/stdlib_strings.html#join)
+    interface join
+        module procedure :: join_string
+        module procedure :: join_char
+    end interface join
+
+
 contains
 
 
@@ -943,5 +965,98 @@ contains
 
     end function zfill_char
 
+    !> Convert a Fortran character string to a C character array
+    !>
+    !> Version: experimental    
+    pure function to_c_string_from_char(value) result(cstr)
+       character(len=*), intent(in) :: value
+       character(kind=c_char) :: cstr(len(value)+1)
+       integer :: i,lv
+       lv = len(value)
+       do concurrent (i=1:lv) 
+           cstr(i) = value(i:i)
+       end do 
+       cstr(lv+1) = c_null_char
+    end function to_c_string_from_char
+
+    !> Convert a Fortran string type to a C character array
+    !>
+    !> Version: experimental    
+    pure function to_c_string_from_string(value) result(cstr)
+       type(string_type), intent(in) :: value
+       character(kind=c_char) :: cstr(len(value)+1)
+       integer :: i,lv
+       lv = len(value)
+       do concurrent (i=1:lv) 
+           cstr(i) = char(value,pos=i)
+       end do 
+       cstr(lv+1) = c_null_char
+    end function to_c_string_from_string    
+
+    !> Joins a list of strings with a separator (default: space).
+    !> Returns a new string
+    pure function join_string(strings, separator) result(cmd)
+        type(string_type), intent(in) :: strings(:)
+        character(len=*), intent(in), optional :: separator
+        type(string_type) :: cmd
+        integer :: ltot, i, lt, pos
+        character(len=:), allocatable :: sep,cmd_char
+        ! Determine separator: use user-provided separator or default space
+        if (present(separator)) then
+            sep = separator
+        else
+            sep = ' '
+        end if
+        ! Calculate the total length required, including separators
+        ltot = sum(len_trim(strings)) + (size(strings) - 1) * len(sep)
+        allocate(character(len=ltot) :: cmd_char)
+
+        ! Concatenate strings with separator
+        pos = 0
+        do i = 1, size(strings)
+            lt = len_trim(strings(i))
+            cmd_char(pos+1:pos+lt) = char(strings(i),1,lt)
+            pos = pos + lt
+            if (i < size(strings)) then
+                cmd_char(pos+1:pos+len(sep)) = sep
+                pos = pos + len(sep)
+            end if
+        end do
+
+        call move(from=cmd_char,to=cmd)
+
+    end function join_string    
+
+    !> Joins a list of strings with a separator (default: space).
+    !> Returns a new string
+    pure function join_char(strings, separator) result(cmd)
+        character(*), intent(in) :: strings(:)
+        character(len=*), intent(in), optional :: separator
+        character(len=:), allocatable :: cmd
+        integer :: ltot, i, lt, pos
+        character(len=:), allocatable :: sep
+        ! Determine separator: use user-provided separator or default space
+        if (present(separator)) then
+            sep = separator
+        else
+            sep = ' '
+        end if
+        ! Calculate the total length required, including separators
+        ltot = sum(len_trim(strings)) + (size(strings) - 1) * len(sep)
+        allocate(character(len=ltot) :: cmd)
+
+        cmd = repeat(' ',ltot)
+        ! Concatenate strings with separator
+        pos = 0
+        do i = 1, size(strings)
+            lt = len_trim(strings(i))
+            cmd(pos+1:pos+lt) = strings(i)(1:lt)
+            pos = pos + lt
+            if (i < size(strings)) then
+                cmd(pos+1:pos+len(sep)) = sep
+                pos = pos + len(sep)
+            end if
+        end do
+    end function join_char
 
 end module stdlib_strings

test/string/test_string_match.f90

@@ -2,7 +2,7 @@
 module test_string_match
     use testdrive, only : new_unittest, unittest_type, error_type, check
     use stdlib_ascii, only : reverse
-    use stdlib_strings, only : starts_with, ends_with
+    use stdlib_strings, only : starts_with, ends_with, join
     use stdlib_string_type, only : string_type
     implicit none
 
@@ -16,7 +16,8 @@ subroutine collect_string_match(testsuite)
 
         testsuite = [ &
             new_unittest("starts_with", test_starts_with), &
-            new_unittest("ends_with", test_ends_with) &
+            new_unittest("ends_with", test_ends_with), &
+            new_unittest("join", test_join) &
             ]
     end subroutine collect_string_match
 
@@ -77,6 +78,32 @@ subroutine check_ends_with(error, string, substring)
         call check(error, ends_with(string_type(string), string_type(substring)) .eqv. match, message)
     end subroutine check_ends_with
 
+    subroutine test_join(error)
+        type(error_type), allocatable, intent(out) :: error
+        character(len=5) :: test_strings(3)
+
+        test_strings = [character(5) :: "one", "two", "three"]
+        call check_join(error, test_strings, " ", "one two three")
+        if (allocated(error)) return
+        call check_join(error, test_strings, ",", "one,two,three")
+        if (allocated(error)) return
+        call check_join(error, test_strings, "-", "one-two-three")
+    end subroutine test_join
+
+    subroutine check_join(error, strings, separator, expected)
+        type(error_type), allocatable, intent(out) :: error
+        character(len=*), intent(in) :: strings(:)
+        character(len=*), intent(in) :: separator
+        character(len=*), intent(in) :: expected
+        character(len=:), allocatable :: joined
+        character(len=:), allocatable :: message
+
+        joined = join(strings, separator)
+        message = "'join' error: Expected '" // expected // "' but got '" // joined // "'"
+        call check(error, joined == expected, message)
+
+    end subroutine check_join
+
     subroutine test_ends_with(error)
         type(error_type), allocatable, intent(out) :: error
         call check_ends_with(error, "pattern", "pat")