Segmentation Fault 11 and trouble creating/printing an array of strings in c

Question

I am working on a project that will require me to keep an array of the 10 most recently entered commands from a user, and created a small test program to ensure I could actually create an array of 10 strings and print it back out. The code copied below generates "Segmentation fault: 11" when run, even though it compiles with no warnings or errors. I am very new to c and I know that this task will require some combination of pointers to arrays of characters, but I cannot seem to get it working. What do I need to do to be able to overwrite the string at any of the 10 indices in 'history' and print the current history array out by calling printFullHistory()?

void printFullHistory(char** history){
    for(int i = 0; i < sizeof(history); i++){
        for(int j = 0; j < sizeof(history)[i]; j++){
            printf("%s", history[i][j]);
        }
    }
}//end printFullHistory

int main(){
    char* history[10];
    strcpy(history[0], "ls");
    printFullHistory(history);
    return 0;
}//end main

Read about the `sizeof` operator, and what is `sizeof(history)[i]` — Iharob Al Asimi, Feb 09 '16 at 14:12
Think about change function to `void printFullHistory(char** history, size_t rows, size_t cols)` — LPs, Feb 09 '16 at 14:15
Also see [How to find the 'sizeof'(a pointer pointing to an array)?](http://stackoverflow.com/questions/492384/how-to-find-the-sizeofa-pointer-pointing-to-an-array) — Lundin, Feb 09 '16 at 14:19

Giorgi Moniava · Answer 1 · 2016-02-09T14:22:34.217

3

sizeof being one of your issues, this is also wrong:

char* history[10];
strcpy(history[0], "ls");

history[0] is not initialized to point to valid memory, you can't write to it.

And besides:

printf("%s", history[i][j]);

history[i][j] refers to j-th letter of i-th string, so maybe you wanted to use %c. Nevertheless, you can't print values of uninitialized variables. If you do, this is undefined behaviour.

edited Feb 09 '16 at 14:22

answered Feb 09 '16 at 14:15

Giorgi Moniava

27,046
9
53
90

score 1 · Answer 2 · answered Feb 09 '16 at 14:16

Two main problems:

You strcpy() to an uninitialized pointer, that invokes undefined behavior. Your need to make the pointer point to valid memory. Either by using malloc()/free() or by making the array two dimensional.
You are using the sizeof operator to determine the size of an array through a pointer to the array, that's wrong. When the operand of sizeof is a pointer the result if the size of the pointer namely sizeof(void *) which is not the size of the array. You can pass the size to the function or, you can add a NULL pointer at the end of the array and iterate until you find it, just the same concept used for strings in c.

Segmentation Fault 11 and trouble creating/printing an array of strings in c

2 Answers2