C Generic Print Array function - printing String Array - c

Question

I'm trying to write a generic printing arrays function in C and somehow it doesn't work well with a String array.
Here's the main:
#define LEN 20
typedef struct {
char name[LEN]; // worker's name
int salary; // worker's salary
char **childArr; // array of children names
int numChildren; // number of children
} Worker;
void printArray(void* arr, int size, int typeSize, void (*print)(void*));
void printString(void* s);
void printWorker(void* worker);
void main() {
// arrays of children's names
char *chBamba[] = { "Bambale1", "Bamb2", "Bamb3", "Bambook4", "Bambookle5" };
char *chBisli[] = { "Bislile1", "Bischick2", "Bislile3", "Bis4"};
int nBamba = sizeof(chBamba) / sizeof(*chBamba);
int nBisli = sizeof(chBisli) / sizeof(*chBisli);
// array of workers
Worker a[] = { {"Printf", 10, NULL, 0}, {"Bisli", 20, chBisli, nBisli},
{"TapooChips", 3, chBamba, nBamba}, {"Bamba", 19, chBamba, nBamba} };
printArray(a, sizeof(a)/sizeof(Worker), sizeof(Worker), printWorker);
}
And the functions:
void printArray(void* arr, int size, int typeSize, void (*print)(void*)) {
int i;
for (i = 0; i < size; i++) {
print((char*)arr+i *typeSize);
}
printf("\n");
}
void printString(void* s) {
char* str = (char*)s;
printf("[ %s ]", *str);
}
void printWorker(void* worker) {
Worker* w = (Worker*)worker;
printf("%s\t %d...(%d) ", w->name, w->salary, w->numChildren);
if (w->numChildren != 0)
printArray(w->childArr, w->numChildren, LEN, printString);
printf("\n");
}
After printing the data of the second worker and going to the "children" array, the code breaks...
any idea why? and how can i fix it?
after editing this: printArray(w->childArr,w->numChildren,sizeof(w->childArr[0]),printString);
and this: printf("[ %s ]",str);
i now have the following print:
img1

Answer 1

This line here:
printArray(w->childArr,w->numChildren,LEN,printString);
You pass LEN as the size of the element in the array, which is probably way bigger than the size of an array element. This makes the loop in printArray go outside the array boundaries, where any access is undefined behavior.
Your array contains pointers to strings. You need to pass sizeof(char*). Or, in a more D.R.Y manner:
printArray(w->childArr, w->numChildren, sizeof w->childArr[0], printString);
Your printString function does the wrong type conversion. You must remember that printArray passes a pointer to the current element into the callback. Since your iterate over an array of char*, it will pass a char**. With that in mind:
void printString(void *vpStr) {
char **pStr = vpStr;
printf("[ %s ]", *pstr);
}

Answer 2

Just for reference, the method you are using is how this is traditionally done in C. But in modern C you can write such generic functions in a better way: type safe and without the need for function pointers:
#include <stdio.h>
#include <string.h>
#define print_array(data, n) \
_Generic((*data), \
int: print_int, \
char: print_char)(data,n) \
void print_int (const int* data, size_t n)
{
for(size_t i=0; i<n; i++)
{
printf("%d ", data[i]);
}
}
void print_char (const char* data, size_t n)
{
for(size_t i=0; i<n; i++)
{
printf("%c ", data[i]);
}
}
int main (void)
{
int int_array [3] = {1, 2, 3};
const char* char_array = "hello world";
print_array(int_array, 3);
printf("\n");
print_array(char_array, strlen(char_array));
printf("\n");
}