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Gnu C - segmentation fault

Posted on 1998-05-05
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Last Modified: 2012-05-04
Hello, I have problems with the following script, in which I tried to "copy" the C library function strtod with the GNU inline assembler:

#include "stdio.h"
#include "stdlib.h"

double TGIstrtod(const char *nptr, char **endptr) {

     long a;
     double returnvalue;
     long b;
     double c;
     long d;
     d = (long)*endptr;
     __asm__ __volatile__(
//here comes the assembler part...
//...
       :"=m" (returnvalue)
       :"S" (nptr), "m" (errno), "m" (a), "m" (b), "m" (c), "m" (d)
       :"eax","ebx","edx");
     *endptr = (char*)d;
     return returnvalue;
}


void main (int argc, char *argv[]){
  char **s;
  *s = ".";
  if (argc > 1) {
     printf("Float: %.10e\n",  TGIstrtod (argv[1],(char **)s));
     printf("%s\n",*s); }
   else printf ("Please run with parameter!!");
}

I get the segmentations fault in the lines *s = "." and if I submit a parameter. I think there's a problem with s, but - being very unfamiliar with C - I don't know why. Any help if greatly appreciated!
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Question by:Christian_Wenz
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3 Comments
 
LVL 51

Accepted Solution

by:
ahoffmann earned 200 total points
ID: 1635066
*s is a pointer, you need to alloc memory befor you assign values
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by:Christian_Wenz
ID: 1635067
this might be it. I also found out that I should replace char **)s by &s and put char *s instead of char **s. But how do I allocate memory?
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LVL 51

Expert Comment

by:ahoffmann
ID: 1635068
...
char *s = NULL;
s = malloc(100); /* replace 100 by an appropriate value */
if (s == NULL) {
  printf("error: malloc failed.\n"); exit(1);
}
...
    TGIstrtod(argv[1], &s)
...

Keep in mind that you allocate enough memory for s (used in
TGIstrtod, 'cause it does not check the size of the given
pointer).
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