使用文件中的字符串数组进行分段错误

Question

I think I get understand how string works, but some how get a segmentation error when try to run this. I'm trying to create array of string that i read from file f. Also any comments for optimisation and or a better way to code (especially using pointer)is appreciated.

char a[700000][120];
char str[120];
int i=0,l,p;
while (fgets(str,120,f)) {
    strcpy(a[i],str);
    i++;
    }
int n=i;
for (i=0;i<=3;i++) {
    printf("%s\n",a[i]);
}

Answer 1

See if this helps

char **a;
int i;

a = malloc(700000 * sizeof(char*));
for (i = 0; i < 700000; i++) {
    a[i] = malloc(120*sizeof(char));
}

// read file here instead
strcpy(a[0],"hello");
strcpy(a[1],"goodbye");
strcpy(a[2],"yes");

for (i=0;i<=3;i++) {
    printf("%s\n",a[i]);
}

Per Michi, remember to free the memory afterwards.

for (i = 0; i < 700000; i++) {
    free(a[i]);
}
free(a);

Appendix Turns out you can check the stack size AND change it. Consider this

struct rlimit rl;
int result;

result = getrlimit(RLIMIT_STACK, &rl);

printf("stack limit %d\n", rl.rlim_cur);
printf("stack limit %d\n", rl.rlim_max);
return 0;

It gives me

stack limit 8388608
stack limit -1

(there is the 8MB).

Answer 2

There is a limit of array allocation, the size u are trying causes stack overflow of the function, because your array can't fit into the memory allocated to the function stack .

There is a limit of 8MB on the maximum size of objects, due to internal compiler implementation limits. You should use malloc() to create large arrays instead.

Answer 3

I think there is no need of creating str variable, you could have used the a itself. Moreover as mentioned in the comments too, try using dynamic memory, as most programmers don't use stack for huge allocations. May be heap may have greater size than stack.

Answer 4

In Linux Environment, ulimit -s can return the stack size.

root@ubuntu:# ulimit -s
8192

It means the max stack space that the system support is 8192 KB , that is 8MB . test program as follows, try to modify array size from 8*1024 to 7*1024.

#include<stdio.h>

void test()
{
}

int main()
{
    char a[7*1024][1024];
    test();
    return 0;
}

Answer 5

You can try this.

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

void main(void) {

    FILE *fp = NULL;
    fp = fopen("read.txt", "rb");
    if(fp == NULL)
        printf("failure\n");
    else
        printf("success\n");

    char buffer[4096];
    while (fgets(buffer, sizeof(buffer), fp) != 0)
        fputs(buffer, stderr);

}