This is likely a very beginner question so please go easy on me…

I have a struct array as follows

struct Data {
   int lineno;
   char* line[10];
}

struct Data datas[20] = {{ 0, NULL }};

I’m trying to deep copy a char * [] into an array element yet I keep getting seg faults.

I’ve attempted the following

for (int i = 0; i < 20; i++) {
    strcpy(datas[slot].line[i], line[i]);
}

but this doesn’t work.
I thought that my problem was attempting to copy null values in line so I tried the following

for (int i = 0; i < 20; i++) {
    if (line[i])
        strcpy(datas[slot].line[i], line[i]);
}

but this doesn’t work either.

>Solution :

You need to allocate memory before copying the string. Most implementations support strdup to both allocate memory and copy the string:

for (int i = 0; i < 20; i++) {
    datas[slot].line[i] = strdup(line[i]);
}

If your implementation doesn’t support strdup, you could create your own:

#include <stdlib.h>
char *StrDup(const char* str) {
    size_t len = strlen(str) + 1;
    char *res = malloc(len);
    if (res) memcpy(res, str, len);
    return res;
}