C ++中的strcpy无法正常工作

Question

Can anyone tell why strcpy in this code returns an empty string?

#include <iostream>

char* strcpy(char* dest, const char* from) {
    for ( ; *from; dest++, from++) {
        *dest = *from;
    }

    return dest;
}

int main() {
    char a[] = "aba";
    char b[] = "hello";
    std::cout << strcpy(a, b);
    return 0;
}

The compiler I'm using is GNU G++11 4.9.2

upd: this doesn't work either #include

char* strcpy(char* dest, const char* from) {
    for ( ; *from; dest++, from++) {
        *dest = *from;
    }

    *dest = '\0';

    return dest;
}

int main() {
    char a[] = "abaaa";
    char b[] = "hello";
    std::cout << strcpy(a, b);
    return 0;
}

Answer 1

Try using temp pointer:

char* strcpy(char* dest, const char* from) {
    char *tmp = dest;
    for ( ; *from; tmp++, from++) {
        *tmp = *from;
    }
    *tmp = '\0';

    return dest;
}

Also consider allocate memory for the dest with appropriate number of characters.

Answer 2

The function and the program itself are invalid.:)

For example array a can not accomodate all characters from array b because its size is less than the size of b . (The size of a is equal to 4 while the size of b is equal to 6)

char a[] = "aba";
char b[] = "hello";

So the call strcpy(a, b) in this statement

std::cout << strcpy(a, b);

results in undefined behaviour.

As for the function then it does not copies the terminating zero from the sourse string to the destination string. And it does not return pointer to the first character of the destination string because inside the function pointer dest is changed (it was increased)

The correct function can look like

char* strcpy( char* dest, const char* from ) 
{
    char *p = dest;

    while ( *p++ = *from++ );

    return dest;
}

Answer 3

Instead of incrementing dest and from in the loop, try this:

 char *StrCpy (char *dest, const char *from){ int i=0; for (i=0;i<strlen(from);i++){ *(dest+i) = *(from+i); } *(dest+(strlen(from)))='\\0'; return dest; }