Using CALL_EXTERNAL with the Cygwin environment

Some Windows developers choose to use the Cygwin GCC port as their compiler. This TechTip describes how to set up IDL so that CALL_EXTERNAL works with GCC.

Several customers have reported success using CALL_EXTERNAL with Cygwin's GCC Windows port instead of Microsoft Visual Studio.

• Create a new user environment variable (Control Panel -> System -> Advanced -> Environment Variables) called IDL_DLM_PATH.

  Set this to: C:\RSI\IDL61\bin\bin.x86;c:\cygwin\bin

• Set the following parameters on !MAKE_DLL:
  1. !make_dll.LD = 'c:\cygwin\bin\ld.exe -shared -o %L %O %X'
  2. !make_dll.CC = 'c:\cygwin\bin\gcc.exe %X -fPIC -I"/cygdrive/c/RSI/IDL61/external/include" -c -D_REENTRANT %C -o %O'
  3. !make_dll.COMPILER_NAME='GCC'
• To test, load and compile the STRING_ARRAY.PRO example in the IDL61\external\call_external\C subdirectory.

  IDL> string_array, 'Hello, Cygwin!', /VERBOSE

  Calling string_array with:

  STRARR_L STRING = 'Hello, Cygwin!'

  Hello, Cygwin!

  Result from string_array is:

  RESULT STRING = 'Hello, Cygwin!'

If the PATH environment does not also include c:\cygwin\bin, users may receive an error message that cygwin1.dll could not be found.