getting "segmentation failed" error in strrev function implementation

Question

void main() { 
    void strrev(char *); 
    char *p="GOOd";
    strrev(p);
    printf("%s",p);
}

void strrev(char *str) { 
    char temp, *end_ptr;
    if( str == NULL || !(*str) ) return;
    end_ptr = str + strlen(str) - 1;

    while( end_ptr > str ) 
    { 
        temp = *str; 
        *str = *end_ptr; 
        *end_ptr = temp; str++; 
        end_ptr--; 
    } 
}

i am getting the error segmentation failed can any one help me out how to sort it out...

Answer 1

The statement:

char *p = "GOOd";

Defines a string literal "GOOD", pointed by an pointer p.

You are trying to modify this string literal through the strrev function which results in Undefined Behavior(UB) and the crash.

The problem with string literals is they are stored in a read-only(Implementation defined) memory location and user programs are not allowed to change that.If a program attempts to do so it causes an UB.

So instead of using a string literal You should use an array.

You should be using:

char p[] = "GOOd";

Answer 2

One problem is that in the following:

char *p = "GOOd";

the compiler is allowed to place the string literal in read-only memory.

Any attempt to modify the string pointed to by p results in undefined behaviour.

Try changing the above line to:

char p[] = "GOOd";

I don't see anything wrong with the strrev() function itself.