Thread: Pass by reference a character pointer in c

Code:

int mystrlen(const char *str)
{
	int len = 0;
	while (*str++)
		len++;
	return len;
}


void main() {

	char *str1 = "Hello";

	printf("\n length = %d \n", mystrlen(str1));
	printf(" str=%s\n", str1);
}

o/p :
length = 5
str=Hello

Here in main function, we call mystrlen() and pass a reference address of str.

In function mystrlen(), we modify/increase(str++) the string pointer till '\0'.
In main() we print the str after function call mystrlen. But string will print whole contents. It will print hello. How is this possible? Because in mystrlen() the pointer pointing to NUL...

How is this possible?

It's happening because you're passing the pointer by value, so you are changing a copy, not the original pointer.

Originally Posted by krishnampkkm

Code:

int mystrlen(const char *str)
{
    int len = 0;
    while (*str++)
        len++;
    return len;
}


void main() {

    char *str1 = "Hello";

    printf("\n length = %d \n", mystrlen(str1));
    printf(" str=%s\n", str1);
}

o/p :
length = 5
str=Hello

Here in main function, we call mystrlen() and pass a reference address of str.

In function mystrlen(), we modify/increase(str++) the string pointer till '\0'.
In main() we print the str after function call mystrlen. But string will print whole contents. It will print hello. How is this possible? Because in mystrlen() the pointer pointing to NUL...

In C everything gets passed by value. But! You can emulate any level of references using pointers. A pointer gives you a reference to a value, a double pointer a reference to a reference to a value, and so on.

Code:

#include <stdio.h>
#include <ctype.h>

void skip_space(char** s)
{
    
    while(isspace(**s))
        (*s)++;
}
int main(void)
{
    char * spacey = "                 <- space starts here";
    skip_space(&spacey);
    puts(spacey);
}