Can pointers be accessed globally in C?

Question

Can I access pointers from any function without sending info from main() to each function? I've tried looking for information but couldn't find an answer.

As long as the function can reach the pointer, either because pointer is global or passed as function variable, then yes. — AntonH, Aug 12 '14 at 19:38
A pointer is a variable like any other. As such, it can only be accessed from other functions if it's a global, same as any other variable. — Mooing Duck, Aug 12 '14 at 19:38
Some sample code to show what you have a hard time understanding would really help. As it is the question is way too broad for anyone to help you. Please read http://stackoverflow.com/help/dont-ask. — Asics, Aug 12 '14 at 19:55
Depends on what you mean by "access a pointer"; are you talking about using a pointer *variable* declared within `main` or elsewhere in the program, or are you talking about accessing a memory location directly (along the lines of `char *p = 0xDEADBEEF;`)? — John Bode, Aug 12 '14 at 20:44

score 2 · Answer 1 · edited May 23 '17 at 11:57

2

Did you try it?

Yes, you can, but using lots of global variables is not a good idea.

edited May 23 '17 at 11:57

Community

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answered Aug 12 '14 at 19:38

We Are All Monica

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It would be trivial to try it. I can't understand why such questions are asked. – Martin James Aug 12 '14 at 20:01

score 0 · Answer 2 · answered Aug 12 '14 at 19:40

0

If the pointer is passed to the function as parameter or it is declared as global then yes.

answered Aug 12 '14 at 19:40

Nanc

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What do you mean by "passed by reference"? There are no references in C. Why does not ordinary pass-by-value suffice? – The Paramagnetic Croissant Aug 12 '14 at 19:43

score 0 · Answer 3 · answered Aug 12 '14 at 19:48

Yes you can, because address of variable - it's her own unique identifier in memory space, like a house address within the big city. And e.g. for debug reasons it can be very helpfull (the only thing you should be sure about - live scope of this variable, because when variable leaves her scope - pointer to this address is no longer valid).

score 0 · Answer 4 · answered Aug 12 '14 at 20:08

As others have said: There are good reasons to not use many globals ("locality of code" is useful), but careful use of globals is justified in some cases. An example might help:

// A slightly contrived example to show how and when you 
// might use a global variable in a C program.
#include <stdio.h>
#include <stdlib.h>

// The following are compile-time constants, and considered
// good coding practice
#define DEBUG_WARN 1
#define DEBUG_ERROR 2

// The following is a global, accessible from any function,
// and should be used cautiously.  Note the convention (not
// universally adopted) of prefixing its name with "g_"
int g_debug_threshold = 0;

// debug_print() uses the global variable to
// decide whether or not to print a debug message.
void debug_print(char *msg, int level) {
  if (level >= g_debug_threshold) {
    fprintf(stderr, "%s\n", msg);
  }
}

void foo() {
  debug_print("hi mom", DEBUG_WARN);
}

int main(int ac, char **av) {
  // Here we set the debug threshold at runtime
  if (ac > 1) {
    g_debug_threshold = atoi(av[1]);
  }
  foo();
}

Can pointers be accessed globally in C?

4 Answers4