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The macro will compile a test program to see whether the compiler does allow new variable declarations in the middle of a C statement block, i.e. after some non-declaration line. New compilers will allow that which makes the behave a bit more like C++ - the gcc did support it for quite a time already.

#define DECLARE_BLOCK_NEEDED says they need to be at the beginning of of a statement block. Additionally two defines DECLARE_BLOCK { and DECLARE_END } are being set. That makes it possible to do the following in your source code (which this macro is really made up for):

 #define ___ DECLARE_BLOCK
 #define ____ DECLARE_END
 int f() {
  char buffer[1024];
  fgets(buffer, 1024, stdin);
  ___ int i; int ii = strlen(buffer);
  for (i=0; i < ii; i++) {
     fputc(buffer[i], stdout);

Source Code

Download the latest version of ax_c_declare_block.m4 or browse the macro’s revision history.


Copyright © 2008 Guido U. Draheim

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