Question

#include <errno.h>  
  /* compress until end of file */
  do {
       strm.avail_in = fread(in, 1, CHUNK, source);
       errno; //<-----DEBUGGER "CXX0017: Error: symbol errno not found"  
       perror("Error:");

      if (ferror(source)) //<--ferror = 32 but there is no string from perror? 
      {
         //error handling

Answer 1

When you build with the DLL version of the CRT (/MDd for example), errno is a macro. Translating it to a function call to obtain the shared value of errno. Fix it like this:

int err = errno;

so you can inspect the value of err.