seg fault caused by malloc and sscanf in a function
- by Framester
Hi,
I want to open a text file (see below), read the first int in every line and store it in an array, but I get an segmentation fault. I got rid of all gcc warnings, I read through several tutorials I found on the net and searched stackoverflow for solutions, but I could't make out, what I am doing wrong.
It works when I have everything in the main function (see example 1), but not when I transfer it to second function (see example 2 further down). In example 2 I get, when I interpret gdb correctly a seg fault at sscanf (line,"%i",classes[i]);.
I'm afraid, it could be something trivial, but I already wasted one day on it.
Thanks in advance.
[Example 1] Even though that works with everything in main:
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
const int LENGTH = 1024;
int main() {
char *filename="somedatafile.txt";
int *classes;
int lines;
FILE *pfile = NULL;
char line[LENGTH];
pfile=fopen(filename,"r");
int numlines=0;
char *p;
while(fgets(line,LENGTH,pfile)){
numlines++;
}
rewind(pfile);
classes=(int *)malloc(numlines*sizeof(int));
if(classes == NULL){
printf("\nMemory error.");
exit(1);
}
int i=0;
while(fgets(line,LENGTH,pfile)){
printf("\n");
p = strtok (line," ");
p = strtok (NULL, ", ");
sscanf (line,"%i",&classes[i]);
i++;
}
fclose(pfile);
return 1;
}
[Example 2] This does not with the functionality transfered to a function:
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
const int LENGTH = 1024;
void read_data(int **classes,int *lines, char *filename){
FILE *pfile = NULL;
char line[LENGTH];
pfile=fopen(filename,"r");
int numlines=0;
char *p;
while(fgets(line,LENGTH,pfile)){
numlines++;
}
rewind(pfile);
* classes=(int *)malloc(numlines*sizeof(int));
if(*classes == NULL){
printf("\nMemory error.");
exit(1);
}
int i=0;
while(fgets(line,LENGTH,pfile)){
printf("\n");
p = strtok (line," ");
p = strtok (NULL, ", ");
sscanf (line,"%i",classes[i]);
i++;
}
fclose(pfile);
*lines=numlines;
}
int main() {
char *filename="somedatafile.txt";
int *classes;
int lines;
read_data(&classes, &lines,filename) ;
for(int i=0;i<lines;i++){
printf("\nclasses[i]=%i",classes[i]);
}
return 1;
}
[Content of somedatafile.txt]
50 21 77 0 28 0 27 48 22 2
55 0 92 0 0 26 36 92 56 4
53 0 82 0 52 -5 29 30 2 1
37 0 76 0 28 18 40 48 8 1
37 0 79 0 34 -26 43 46 2 1
85 0 88 -4 6 1 3 83 80 5
56 0 81 0 -4 11 25 86 62 4
55 -1 95 -3 54 -4 40 41 2 1
53 8 77 0 28 0 23 48 24 4
37 0 101 -7 28 0 64 73 8 1
...
