Try to convert all strings in argv[] to integers and store them into a new array

user_15776183 0
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I'm new to C and I'm trying to convert all strings that the user typed in the command line to integers and store them into a new array, so that I can use it later. But I get a "segmentation fault (core dumped)" issue.

Can someone check with my code and point out the error(s)?

int main(int argc, char *argv[]) {
    long int conv[argc - 1];
    for (int i = 0; i < argc; i++) {
        conv[i] = strtol(argv[i + 1], NULL, 10);
    }

If I run this program like, ./main 1 2 3, then {1, 2, 3} should be stored in the new array of integers.

c
2 Answers

The arguments you pass in to your program are stored in argv[1] to argv[argc-1], so you'd want to change the for loop to something like this: for (int i = 1; ...) {...}. Also, with strtol(argv[i+1],NULL,10);, when i==argc-1, you're trying to access the array out of bounds.

Here's a modified version of your code with the fixes applied:

int main(int argc, char *argv[]){
    long int conv[argc-1];
    for(int i=1;i<argc;i++){
        conv[i-1]=strtol(argv[i],NULL,10);
    }
}
user_108786230

Your loop attempts to access an "out-of-bounds" array element on its last iteration: if you run the program with, say, ./main 1 2 3, then argc will be 4 and the last argument will be in argv[3]. However, when the loop index, i is 3, the loop will still run and you will be attempting to read argv[i + i] – which is argv[4] and thus beyond the end of the array.

You can simplify your loop (or, at least, rewrite it) to use the actual i value for the argv index and i - 1 for the conv index; but, of course, you then need to start the loop with i = 1:

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

int main(int argc, char* argv[])
{
    long int conv[argc - 1];
    for (int i = 1; i < argc; i++) {
        conv[i - 1] = strtol(argv[i], NULL, 10);
    }
    // Data check:
    for (int j = 0; j < argc - 1; ++j) {
        printf("Data %d is %ld\n", j, conv[j]);
    }
    return 0;
}
user_108710730
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