terminated by signal SIGSEGV (Address boundary error) when running program that uses pointers

Question

. I am trying to make a program similar to 'ls', and I use pointers for doing some stuff. For some reason, when I run it I get terminated by signal SIGSEGV (Address boundary error) . why? I'm new to C and pointers so I don't know what is going on here. the problem is with newColl, because it worked b4 I added it.

the relevant parts of my code:

char newColl(int columns, int* counter) {
    if (columns == *counter) {
        *counter = 0;
        return '\n';
    }

    return ' ';
}

int main(int argc, char* argv[]) {
    char path[256] = ".";  // MAKE STRLEN OF ARG
    int all = 0;
    int columns = 1;
    int collCounter = 0;

    DIR* dir = opendir(path);
    if (dir == NULL) return 1;

    struct dirent* entity;
    entity = readdir(dir);
    
    while (entity != NULL) {
        if (all != 1 && entity->d_name[0] != '.')
            printf("%s%s", entity->d_name, newColl(columns, &collCounter));
        if (all == 1)
            printf("%s%s", entity->d_name, newColl(columns, &collCounter));
        entity = readdir(dir);
        collCounter++;
    }

    return 0;
}

Answer 1

You are invoking undefined behavior by passing data having wrong type to printf() .

The format specifier %s expects char* , but the function newColl returns char .

You should use %c specifyer to print one character represented by an integer.

Wrong:

printf("%s%s", entity->d_name, newColl(columns, &collCounter));

Corrected:

printf("%s%c", entity->d_name, newColl(columns, &collCounter));

Answer 2

What you need:

printf("%s%c", entity->d_name, newColl(columns, &collCounter));

What you did:

printf("%s%s", entity->d_name, newColl(columns, &collCounter));

The format specifier %s expects char* . The function newColl() returns char , which is implicitly cast to int and used as an address to fetch the contents at that location, resulting in SIGSEGV(Address boundary error) .

Check the compiler warnings.

warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
             printf("%s%s", entity->d_name, newColl(columns, &collCounter));