C++ String Methods

In this page:

Finding String Length
Checking if Empty
Finding Substrings
Modifying Strings
Getting Substrings

Finding String Length

.length() and .size() are functionally identical and both return the exact number of characters currently stored in a std::string — .size() exists for consistency with other STL containers, while .length() reads a bit more naturally for strings specifically, but you can use either interchangeably.

Example: Finding String Length

cpp

#include <iostream>
#include <string>

int main() {
	std::string s = "Hello";
	std::cout << s.length() << " " << s.size() << std::endl;
	return 0;
}

Checking if Empty

.empty() returns true if a string has zero characters and false otherwise, and it's generally preferred over checking str.length() == 0, since it reads clearly as a direct yes/no question and can be marginally more efficient for some string implementations.

Example: Checking if Empty

cpp

#include <iostream>
#include <string>

int main() {
	std::string s = "";
	std::cout << (s.empty() ? "empty" : "not empty") << std::endl;
	return 0;
}

Finding Substrings

.find(substring) searches the string for the first occurrence of a given substring and returns the index where it starts, or the special constant string::npos if no match exists anywhere in the string — always check the result against npos before using it, since a failed search doesn't throw an error, it just returns that sentinel value.

Example: Finding Substrings

cpp

#include <iostream>
#include <string>

int main() {
	std::string s = "Hello, world";
	std::cout << s.find("world") << std::endl;
	return 0;
}

Modifying Strings

.append() adds text to the end of a string, .insert(pos, text) injects text at a specific index shifting the rest of the string over, and .erase(pos, count) removes a given number of characters starting at a position — together these give you full control over building and editing strings piece by piece.

Example: Modifying Strings

cpp

#include <iostream>
#include <string>

int main() {
	std::string s = "Hello";
	s.append(", world");
	s.insert(0, ">> ");
	std::cout << s << std::endl;
	return 0;
}

Getting Substrings

.substr(start, length) extracts a copy of part of the string, starting at index start and taking up to length characters (or everything to the end if length is omitted) — the original string is left completely unchanged, since .substr() always returns a brand-new string rather than modifying in place.

Example: Getting Substrings

cpp

#include <iostream>
#include <string>

int main() {
	std::string s = "Hello, world";
	std::cout << s.substr(7, 5) << std::endl;
	return 0;
}

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