在C中追加字符串到字符串？

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

int main()
{
    char str1[] = "Hello, ";
    char str2[] = "World!";
    char str3[100];

    strcat(str3, str1);
    strcat(str3, str2);

    printf("str3: %s\n", str3);
    return 0;
}

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

int main()
{
    char str1[] = "Hello, ";
    char str2[] = "World!";
    char str3[100];

    strcpy(str3, str1);
    strcat(str3, str2);

    printf("str3: %s\n", str3);
    return 0;
}