Question

How do I “include” a string into another string in C ?

Here is an example :

string1 = "www.google";
string2 = "http://"+string1+".com";

I’m having difficulties with strcat().

Thanks

Answer 1

You can use snprintf and its feature to return the size it would need if it had the space available:

const char *string1 = "www.google";
char *string2;
size_t length;

length = snprintf(NULL, 0, "http://%s.com", string1);
if (length < 0) {
    // Handle error.
} else {
    string2 = malloc(length + 1);
    snprintf(string2, length + 1, "http://%s.com", string1);
}

Slightly different variant which avoids having the format string two times:

const char *string1 = "www.google";
const char *format = "http://%s.com";
char *string2;
size_t length;

length = snprintf(NULL, 0, format, string1);
if (length < 0) {
    // Handle error.
} else {
    string2 = malloc(length + 1);
    snprintf(string2, length + 1, format, string1);
}