CODEWITHSUNDEEP
c
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Reputation: 21

Seg Faulting Double Pointer, Correctly Malloced (I believe)

Ok, here's some overview about what I'm trying to achieve. I want the user to be able to enter any amount of strings, and then I want to save those strings in a double char pointer. At the moment I haven't dealt with scaling my memory allocation for my double char pointer because I want to get it working first.

char **list = malloc(sizeof(char*)*5);

for(i = 1; i < argc; i++) {
        strcpy(list[i], argv[i]);
}

I honestly thought this was going to be simple, so hopefully I'm making some stupid mistake. I keep receiving a seg fault error at the strcpy function.

Upvotes: 1

Views: 79

Answers (3)

sirgeorge
sirgeorge

Reputation: 6531

What you did is only allocated memory for array of pointers to strings (which is correct), but you also need to allocate memory for each string in your array:

First (simpler) option:

char **list = malloc(sizeof(char*) * argc);
for(i = 1; i < argc; i++)
{
    list[i] = strdup(argv[i]);
}

second (more complex) option:

size_t n = 0;
char **list = malloc(sizeof(char*) * argc);
for(i = 1; i < argc; i++)
{
    n = strlen(argv[i]) + 1;
    list[i] = malloc(n);
    strcpy(list[i],argv[i]));
}

Upvotes: 3

twain249
twain249

Reputation: 5706

It's not correctly malloced you only malloced the main pointer not the other ones.

Try this

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main(int argc, char **argv) {
    char **list = malloc(sizeof(char*)*argc);
    int i;    
    for(i = 0; i < argc-1; i++) {
       list[i] = malloc(sizeof(char) * (strlen(argv[i+1]) + 1));
       strcpy(list[i], argv[i+1]);
       printf("%s\n", list[i]);
    }
return 0;
}

EDIT I forget the v in argv

EDIT (working copy edited above) output below

./temp hello this is a list of arguments
hello
this
is
a
list
of
arguments

Upvotes: 0

Carl Norum
Carl Norum

Reputation: 224944

You've allocated an array of pointers to strings, but you haven't allocated any space for the strings themselves. Every time you call strcpy(), you're passing it an uninitialized destination pointer. Add a line to the beginning of your loop:

list[i] = malloc(strlen(argv[i]) + 1);

If you want it to work for any number of strings, your initial allocation has to be:

char **list = malloc(sizeof(char *) * argc);

Upvotes: 0

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