Thread: how to replace a substring in a string

How can I replace a substring within a string? For example, if a line consists of different words separated from each other by comma, such as in:
file,tcp,ftp,SF,5,6,3,normal.
How can I locate the second word (identified by 1st and 2nd commas) and replace that word with a number of my choice?

Or using std::string, which is a bit clearer (for me, at least)

Code:

#include <iostream>
#include <string>

// good std::string documentation here http://www.cppreference.com/cppstring.html

int main() {
	typedef std::string::size_type size_type;
	std::string test("file,tcp,ftp,SF,5,6,3,normal");
	std::string replacement("udp");

	// find returns position of comma, one more is passed that
	size_type firstIndex = test.find(',') + 1;
	size_type secondIndex = test.find(',', firstIndex);

	// see if we found two commas
	if (firstIndex == std::string::npos || secondIndex == std::string::npos) {
		std::cout << test << " not valid format" << std::endl;
		return 0;
	}

	// second parameter is length, not ending spot
	test.replace(firstIndex, secondIndex - firstIndex, replacement);
	
	std::cout << test << std::endl;
	
	return 0;
}

Code:

first_cut = strchr (string, ',');
cut_end = strchr (first_cut, ',');
strcpy (holder, cut_end);
strcpy (++first_cut, newVal);
strcat (first_cut, holder);

Be sure to check that both calls to strchr succeeded or you will be dealing with NULL pointers. In such a situation strcpy will choke.

-Prelude