Question

C does not make this easy. I looked all over, found nothing.

I need to search a C string for a substring starting with “Sample: “, then create a new c string that consists of all the characters after that until the first newline.

In C++ I could do this in a heartbeat. Can a more experienced C programmer show me the way?

I’m sure i could do this by writing it out by hand, but surely there are SOME built-in functions that help?

Answer 1

strstr() and strndup() are your friends, just remember to free the output when you are done:

const char *input = "Hello Sample: This is a test\nTest";

const char *start = strstr(input, "Sample: ");

if (!start)
{
    // report error here
}

const char *end = strstr(start, "\n");
if (!end)
{
    // you have two options here. 
    // #1: use pure strdup on start and you have your output
    // #2: make this an error, and report it to the user.
}


int length = end - start;

char *output = strndup(start, length);

printf("%s", output); // Prints "Sample: This is a test"

free(output);

It isn’t too hard if you know the right API calls.