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Old 10-16-2006, 06:49 AM   #1
mesh2005
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Unhappy strcat segmentation fault


I made a simple c program to create some files on the form sample1, sample2, sample3 ,....
I got segementation fault, I don't know why. Can anyone help me to do it using C (not C++) ?

#include <stdio.h>
#include <stdlib.h>

int main (int argc , char *argv[])
{
int i =0;
FILE *fp;
for (i=0 ; i< 10 ; i++)
{
fp = fopen (strcat("sample",i) , "wb");
fclose(fp);
}
}
 
Old 10-16-2006, 07:13 AM   #2
ntubski
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Quote:
char *strcat(char *dest, const char *src);

DESCRIPTION
The strcat() function appends the src string to the dest string over-
writing the `\0' character at the end of dest, and then adds a termi-
nating `\0' character. The strings may not overlap, and the dest
string must have enough space for the result.
strcat writes to the buffer pointed to by the first argument. Since you are putting a constant string, it is overwriting past the end, thus the segfault. You need to use a buffer with some space for writing extra letters:
Code:
int main (int argc , char *argv[])
{
int i =0;
FILE *fp;
char filename[16] = "sample";
   for (i=0 ; i< 10 ; i++)
   {
 //strncat doesn't write more characters than the 3rd argument
      fp = fopen (strncat(filename,i, sizeof(filename)-6) , "wb");
      fclose(fp);
   }
}
 
Old 10-16-2006, 07:14 AM   #3
tronayne
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Try something like this instead:
Code:
#include <stdio.h>
#include <stdlib.h>

int     main    (int argc, char *argv [])
{
        char    fname [FILENAME_MAX];
        int     i;
        FILE    *fp;

        for (i = 0; i < 10; i++) {
                (void) sprintf (fname, "sample%02d", i);
                if ((fp = fopen (fname, "w")) == (FILE *) NULL) {
                        (void) fprintf (stderr,
                            "%s:\tcan't open %s\n",
                            argv [0], fname);
                        exit (EXIT_FAILURE);
                }
                /*      close the input file            */
                if (fclose (fp)) {
                        (void) fprintf (stderr,
                            "%s:\tcan't close %s\n",
                            argv [0], fname);
                }
        }
        exit (EXIT_SUCCESS);
}

Last edited by tronayne; 10-16-2006 at 09:50 AM. Reason: Get the spacing right
 
Old 10-16-2006, 07:25 AM   #4
Wim Sturkenboom
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And another problem that you will have is that i is an integer. You can not add an integer to a string, unless you use tronayne's solution above (sprintf).
 
Old 10-16-2006, 07:59 AM   #5
mesh2005
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Thank you all
 
  


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