C String: Copy String (Simple Note)

Simple Note

Code

#include <stdio.h>
#include <string.h>
/**
 * 
 * Tested with Dev-C++ 4.9.9.2
 *  
 * Practice of string copy and concat.
 * char * strcpy ( char * destination, const char * source );
 *         copy source to destination
 * char * strncpy ( char * destination, const char * source, size_t num );
 *         copy first n (the specified num) char
 *         from source to destination
 * memset ( void * ptr, int value, size_t num );
 *        Sets the first n (the specified num) bytes of the
 *          block of memory pointed by ptr to the specified value
 *        (interpreted as an unsigned char).
 * 
 */
int main () {
    // a char array without '\0'
    char chArr[4] = {'a', 'b', 'c', 'd'};
    char chArrTwo[6] = "mnopq";
    char chArrThree[6];
    char chArrFour[6];

    // copy chArr to chArrThree
    // will not add '\0' automatically
    strcpy(chArrThree, chArr);
    printf("chArrThree terminate with \\0? %s \n", (chArrThree[4] == '\0'? "true" : "false"));
    // output chArrThree, may contains wrong value since no \0
    printf("%s\n", chArrThree);


    // add \0 manually
    chArrThree[4] = '\0';
    // copy (replace) first Three char of chArrTwo to chArrThree
    strncpy(chArrThree, chArrTwo, 2);
    printf("chArrThree terminate with \\0? %s \n", (chArrThree[4] == '\0'? "true" : "false"));
    // output chArrThree correctly
    printf("%s\n", chArrThree);

    // use memset to preset all chars in chArrFour to \0
    memset(chArrFour, '\0', sizeof(chArrFour));
    // copy chArr to chArrFour
    strncpy(chArrFour, chArr, sizeof(chArr));
    // NOTE:
    // use strncpy will not clear all specified '\0' --> correct
    // use strcpy as below will clear all specified '\0' --> cause wron string
    // strcpy(chArrFour, chArr);
    printf("chArrFour terminate with \\0? %s \n", (chArrFour[4] == '\0'? "true" : "false"));
    // output chArrFour correctly
    printf("%s\n\n", chArrFour);

    system("PAUSE");
}

Result

References

strcpy
http://www.cplusplus.com/reference/cstring/strcpy/

strncpy
http://www.cplusplus.com/reference/cstring/strncpy/

memset
http://www.cplusplus.com/reference/cstring/memset/

Download

Source code at github
https://github.com/benbai123/C_Cplusplus_Practice/blob/master/C_StringProcessing/string_copy.c