C函数返回串联字符串

Question

I am attempting to create a function in C to return a string that is the result of concatenating two smaller strings. My code looks like this:

const char *concat(char* s1, char* s2){
    char ns[strlen(s1) + strlen(s2) + 1];
    ns[0] = '\0';
    strcpy(ns, s1);
    strcpy(ns, s2);
    return ns;
}

I understand that the string ns exists only within the scope of the function and cannot be returned, but a pointer string would not be editable and would defeat the purpose of the function. Is there a better way to do this or is the function fundamentally flawed?

Answer 1

You can use this example, using strcat() is very simple way:

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

void concat(char* s1, char* s2, char* ns) {
    ns[0] = '\0';
    strcpy(ns, s1);
    strcat(ns, s2);
}

int main(int argc, char const *argv[])
{
    char* s1="hola";
    char* s2 =" mundo";
    char s3[strlen(s1) + strlen(s2) + 1];
    concat(s1, s2, s3);

    printf("\n%s",s3);
    printf("\n");
    return 0;
}

find more info here

Answer 2

Solved by using malloc() to create a dynamic string in heap memory:

const char *concat(char* s1, char* s2){
    char *ns = malloc(strlen(s1) + strlen(s2) + 1);
    ns[0] = '\0';
    strcat(ns, s1);
    strcat(ns, s2);
    return ns;
}

Make sure to free() the memory afterwards, though.

Answer 3

The C function that concatenates two string is strcat!

int main(void)
{
    char *s1="Good ";
    char *s2="luck";

    char ns[12];

    strcpy(ns,s1);
    strcat(ns,s2);

    printf("%s\n",ns);

    return 0;
}

You may also use strcat in this way:

strcpy(ns,s1);
printf("%s\n", strcat(ns,s2));