CODEWITHSUNDEEP
cstringstrcpy
Subbu
Subbu

Reputation: 2101

strcpy () not working properly

I am currently writing a program where i was stuck in a different kind of behaviour of strcpy() function . Here is short demo of it...

I went through the following question : Strip first and last character from C string

//This program checks whether strcpy() is needed or not after doing the modification in the string 
#include <stdio.h>
#include <string.h>

int main()
{
        char mystr[] = "Nmy stringP";
        char *p = mystr ;
        p++;

        p[strlen(p)-1] = '\0';
        strcpy(mystr,p);
        printf("p : %s mystr: %s\n",p,mystr);

}

Output :-

p : y strnng mystr: my strnng

If i dont use strcpy() function , then i get 

p : my string mystr : Nmy string

Why is this happening ??

Upvotes: 2

Views: 3108

Answers (2)

Abhineet
Abhineet

Reputation: 5389

You can not use strcpy with overlapping memory locations i.e., if source and destination strings overlap. In this case, the behavior is undefined as stated in the standards.

But you can use a temp memory location to do the swap like this

Upvotes: 1

cnicutar
cnicutar

Reputation: 182619

The standard says:

7.24.2.3

If copying takes place between objects that overlap, the behavior is undefined.

You could use memmove or a different method altogether.

Upvotes: 10

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