c - behaviour of malloc(0)

Question

int main()
{
    char *p;
    p = (char* ) malloc(sizeof(char) * 0);
    printf("Hello Enter the data without spaces :
");
    scanf("%s",p);
    printf("The entered string is %s
",p);
    //puts(p);
}

On compiling the above code and running it , the program is able to read the string even though we assigned a 0 byte memory to the pointer p .

What actually happens in the statement p = (char* ) malloc(0) ?

Answer 1

It is implementation defined what malloc() will return but it is undefined behavior to use that pointer. And Undefined behavior means that anything can happen literally from program working without glitch to a crash, all safe bets are off.

C99 Standard:

7.22.3 Memory management functions
Para 1:

If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.