Calling a function doesn't execute the print statement inside that function

Question

Why is it that my first block of code doesn't output anything while the 2nd block does print out "hi"? I suspect that the program never goes into the test() function in the first block, but I don't know why that happens and how I should fix it.

PS I know that my codes don't really make any sense such as that the return value of the functions should be char *. This is because I haven't completed the function and I am still at the stage of testing what I have written. I think the return value of char * shouldn't be the reason for my problem, but do let me know if it is!

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

char* test(char **strs, int strs_sz){
  printf("%s", "hi");
}

int main(void){
    char *arg[] = {"XX", "YY", "ZZ"};
    char *all = test(arg, 1); 
    printf("%s\n", all);
    free(all);
}

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

char* fcn(char **para){
    printf("%s", "hi");
}

int main(void){
  char *arg[] = {"XX", "YY", "ZZ"};
  char *s = fcn(arg); 
}

Answer 1

To sum up what was already explained in the comments and fill in some blanks:

When using standard C library functions to work with files ( printf actually works with a file stdout ), the data is first cached in memory, and only written to the actual file when some condition is met:

• The file is closed
• The file is fflush ed.
• The memory buffer is full
• etc.

In case of stdout , this will happen when the \n character is printed or when your program exists and the file is closed.

However, in your first code snippet you try to dereference (use) a pointer all .
Since you did not write a return statement in your test function, it is impossible to predict what value will end up being stored in all .

So, your program most likely crashes unexpectedly, and thus the buffer never gets written to stdout .

You should never test incomplete functions!
At the very least, build up a skeleton code that makes the function legal, such as a dummy return statement.

Otherwise, you will encounter "undefined behavior", which is another way of saying your program will react in weird and unpredictable ways.