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Logging in shared file

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# 8  
Old 10-03-2013
I've explored that there are big difference between
Code:
{         va_start( args, format );      length = vsnprintf( buffer, BUF_LEN, format, args );
    
    if (length >= BUF_LEN )
    { 
     expandBuffer(buffer, length + 1);  
     length = vsnprintf(buffer, length + 1, format, args );     }         va_end( args ); }

and
Code:
{    
    va_list args2;     va_start( args, format );     va_copy(args2,args);
    length = vsnprintf( buffer, BUF_LEN, format, args );
    
    if (length >= BUF_LEN )
    { 
     expandBuffer(buffer, length + 1);  
     length = vsnprintf(buffer, length + 1, format, args2 );     }         va_end( args ); }

The first variant doesn't work if the second vsnprintf is called. vsnprintf spoil the args.
# 9  
Old 10-05-2013
What platform and O/S are you running on? Because I don't think that should happen.

That sounds like your stack is getting corrupted, and that's not good.
# 10  
Old 10-14-2013
Linux Red Hat. I've build it also on openvms alpha 8.3. May be I can check it on a small example, where a stack corruption will be practically impossible.

---------- Post updated at 05:25 AM ---------- Previous update was at 04:44 AM ----------

So the experiment:
1. Without copying
main.c
Code:
void vprintf2x(char * format, va_list args)
{
  vprintf(format, args);
  vprintf(format, args);
}

void printf2x(char * format, ...)
{
  va_list args;
  va_start(args, format);
  vprintf2x(format, args);
  va_end(args);
}


int main()
{
  printf2x("%s - %s", "123", "321\n");
  return 0;
}

Result:
$ ./a.out
123 - 321
Segmentation fault


2. With copying
main.c
Code:
#include <stdio.h>
#include <stdarg.h>

void vprintf2x(char * format, va_list args)
{
  va_list args2;
  va_copy(args2, args);
  vprintf(format, args);
  vprintf(format, args2);
  va_end(args2);
}

void printf2x(char * format, ...)
{
  va_list args;
  va_start(args, format);
  vprintf2x(format, args);
  va_end(args);
}


int main()
{
  printf2x("%s - %s", "123", "321\n");
  return 0;
}

Result:
$ ./a.out
123 - 321
123 - 321
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