Thread: Passing pointers to strings to functions

Here is a quick example:

Code:

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

void first(char*);
void second(char*);

int main(void){

	char string[]= "Text has not changed";
	printf("Main: %s\n", string);
	first(string);
	printf("In main: %s\n", string);

	getchar();
	return (0);
}
void first(char *firstString){

	strcpy(firstString, "First Change");
	printf("In first: %s\n", firstString);
	second(firstString);
}
void second(char* secondString){

	strcpy(secondString, "Second Change");
	printf("In second: %s\n", secondString);
}

One minor thing to note here:

Code:

char array[] = "123456789";

That gives you 10 characters. You can't put more in. You can put less in, but you can't put more in. It only allocates 10 spaces for you (one for each non-nul character, + the nul on the end). Not to be confused with this:

Code:

char array[9] = "123456789";

Which specifically allocates 9 characters (you can't put more here either, this is just another fun thing C does with character arrays), but not a nul on the end.


Quzah.

Originally Posted by drclark

Hi,
I have the basic pointers stuff down but have trouble passing the pointer to a string to a function which then passes it to another function for editing, both functions then return and the change should be displyed in a message box.

Like this....

Code:

#include <windows.h>
#include <string.h>


void FirstFunction(char *first);
void SecondFunction(char *second);

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
 	char szText[] = "The Text Has Not Changed";

	FirstFunction(szText);

	MessageBox(NULL, szText, "Note:", MB_OK | MB_ICONINFORMATION);


	return 0;
}

void FirstFunction(char *first)
{
	strcpy(first, "Text Half Changed");
	MessageBox(NULL, first, "Info", MB_OK | MB_ICONINFORMATION);
	SecondFunction(*first);

}

void SecondFunction(char *second)
{
	strcpy(second, "The Text Has Changed");

}

Your version fails because you are trying to change a string literal and no decent compiler is going to let you do that.
The message boxes won't come up because you haven't included windows.h
Also you have to compile and linke the program in GUI mode before it's going to even build correctly.

Is there a good tutorial that someone could reccomend? I have looked all over and can only find stuff on passing a pointer to a function once.\
Thanks

Any basic C tutorial is going to cover passing strings to functions.