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From: Waldemar Schultz <schultz AT ma DOT tum DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: gcc bug or am I blind?
Date: Wed, 12 Dec 2001 12:37:46 +0100
Organization: [posted via] Leibniz-Rechenzentrum, Muenchen (Germany)
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Hi,
Please have a look on this program

//M_CAT.c
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <conio.h>

char *m_strcat(char *base, ...){
va_list arg_ptr;
char *dest;
char *arg;

 printf("%s\n",base);
 if(!base) return NULL;
 dest=strdup(base);
 if(!dest) return NULL;
 va_start(arg_ptr,base);
 for(;;)
 {
  arg=va_arg(arg_ptr,char *);
  if(!arg || !*arg) break;
  printf("'%s':'%s'%ld\n",dest,arg,strlen(arg));getch();
  dest=realloc(dest,strlen(arg)*sizeof(*dest));
  if(!dest)
   break;
  strcat(dest,arg);
 }
 va_end(arg_ptr);
 return dest;
}

int main(void){
char *a="hello ", *b="out ", *c="there ";
char *s;

 s=m_strcat("hello ","out ","there ",NULL);
 if(s)
 {
  printf("%s\n",s); printf("%p\n",s);
  free(s);
 }
 s=m_strcat("HI",a,b,c,NULL);
 if(s)
 {
  printf("%s\n",s); printf("%p\n",s);
  free(s);
 }
 return EXIT_SUCCESS;
}
//M_CAT.c

compiling and running gives the following:

#66:W98 C:\USR\FGSM\H2O\SIM\TOOL>gcc -W -Wall -g m_cat.c

#66:W98 C:\USR\FGSM\H2O\SIM\TOOL>a
hello
'hello ':'out '4
'hello out ':'there '6
hello out there
20b30
HI
Exiting due to signal SIGSEGV
General Protection Fault at eip=00004633
eax=20657255 ebx=00020b3c ecx=00020b4c edx=00020b44 esi=00000008
edi=00000008
ebp=006b6f5c esp=006b6f4c program=C:\USR\FGSM\H2O\SIM\TOOL\A.EXE
cs: sel=00a7  base=82d93000  limit=006b6fff
ds: sel=00af  base=82d93000  limit=006b6fff
es: sel=00af  base=82d93000  limit=006b6fff
fs: sel=0087  base=0000c680  limit=0000ffff
gs: sel=00bf  base=00000000  limit=0010ffff
ss: sel=00af  base=82d93000  limit=006b6fff
App stack: [006b7000..00637000]  Exceptn stack: [00011ebc..0000ff7c]

Call frame traceback EIPs:
  0x00004633 _malloc+99
  0x00002fea _strdup+90
  0x000015bc _m_strcat+56, line 15 of m_cat.c
  0x00001729 _main+145, line 42 of m_cat.c
  0x00002b52 ___crt1_startup+178

#66:W98 C:\USR\FGSM\H2O\SIM\TOOL>symify a.exe

#66:W98 C:\USR\FGSM\H2O\SIM\TOOL>gcc -v
Reading specs from e:/djgpp/lib/gcc-lib/djgpp/2.953/specs
gcc version 2.95.3 20010315/djgpp (release)

can anyone see somthing I am doing wrong?
or is there an issue with varargs ?

Thank you for any help.

-- 
 Gruss Waldemar Schultz.         schultz AT ma DOT tum DOT de
 Technische Universität München, Zentrum Mathematik M1, D 80290 München
 Tel: +49 (0)89 2892 8226        FAX: +49 (0)89 2892 8228