CODEWITHSUNDEEP
cmemcpystrcpy
Sachin
Sachin

Reputation: 21891

strcpy vs. memcpy

What is the difference between memcpy() and strcpy()? I tried to find it with the help of a program but both are giving the same output.

int main()
{
    char s[5] = { 's', 'a', '\0', 'c', 'h' };
    char p[5];
    char t[5];
    strcpy(p, s);
    memcpy(t, s, 5);
    printf("sachin p is [%s], t is [%s]", p, t);
    return 0;
}

Output

sachin p is [sa], t is [sa]

Upvotes: 99

Views: 138129

Answers (9)

abhijeet keshri
abhijeet keshri

Reputation: 11

printf("%s",...) stops printing the data when null is encountered, so both the outputs are same.

The following code differentiates between strcpy and memcpy: 

#include<stdio.h>
#include<string.h>

int main()
{
    char s[5]={'s','a','\0','c','h'};
    char p[5];
    char t[5];
    int i;
    strcpy(p,s);
    memcpy(t,s,5);
    for(i=0;i<5;i++)
        printf("%c",p[i]);
        printf("\n");
    for(i=0;i<5;i++)
        printf("%c",t[i]);

    return 0;
}

Upvotes: 1

Yann Ramin
Yann Ramin

Reputation: 33187

strcpy stops when it encounters a NUL ('\0') character, memcpy does not. You do not see the effect here, as %s in printf also stops at NUL.

Upvotes: 118

Jeremy Friesner
Jeremy Friesner

Reputation: 73081

The main difference is that memcpy() always copies the exact number of bytes you specify; strcpy(), on the other hand, will copy until it reads a NUL (aka 0) byte, and then stop after that.

Upvotes: 6

Thomas Jones-Low
Thomas Jones-Low

Reputation: 7161

Because of the null character in your s string, the printf won't show anything beyond that. The difference between p and t will be in characters 4 and 5. p won't have any (they'll be garbage) and t will have the 'c' and 'h'.

Upvotes: 4

euccas
euccas

Reputation: 775

  • Behavior difference: strcpy stops when it encounters a NULL or '\0'
  • Performance difference: memcpy is usually more efficient than strcpy, which always scan the data it copies

Upvotes: 3

Jaspar L.
Jaspar L.

Reputation: 41

The problem with your test-program is, that the printf() stops inserting the argument into %s, when it encounters a null-termination \0. So in your output you probably have not noticed, that memcpy() copied the characters c and h as well.

I have seen in GNU glibc-2.24, that (for x86) strcpy() just calls memcpy(dest, src, strlen(src) + 1).

Upvotes: 3

Viswesn
Viswesn

Reputation: 4880

strcpy copies character from source to destination one by one until it find NULL or '\0' character in the source.

while((*dst++) = (*src++));

where as memcpy copies data (not character) from source to destination of given size n, irrespective of data in source.

memcpy should be used if you know well that source contain other than character. for encrypted data or binary data, memcpy is ideal way to go.

strcpy is deprecated, so use strncpy.

Upvotes: 10

egrunin
egrunin

Reputation: 25053

what could be done to see this effect

Compile and run this code:

void dump5(char *str);

int main()
{
    char s[5]={'s','a','\0','c','h'};

    char membuff[5]; 
    char strbuff[5];
    memset(membuff, 0, 5); // init both buffers to nulls
    memset(strbuff, 0, 5);

    strcpy(strbuff,s);
    memcpy(membuff,s,5);

    dump5(membuff); // show what happened
    dump5(strbuff);

    return 0;
}

void dump5(char *str)
{
    char *p = str;
    for (int n = 0; n < 5; ++n)
    {
        printf("%2.2x ", *p);
        ++p;
    }

    printf("\t");

    p = str;
    for (int n = 0; n < 5; ++n)
    {
        printf("%c", *p ? *p : ' ');
        ++p;
    }

    printf("\n", str);
}

It will produce this output:

73 61 00 63 68  sa ch
73 61 00 00 00  sa

You can see that the "ch" was copied by memcpy(), but not strcpy().

Upvotes: 143

fbrereto
fbrereto

Reputation: 35925

strcpy terminates when the source string's null terminator is found. memcpy requires a size parameter be passed. In the case you presented the printf statement is halting after the null terminator is found for both character arrays, however you will find t[3] and t[4] have copied data in them as well.

Upvotes: 14

Related Questions