Remove last n characters from a string in C++
This post will discuss how to remove the last n characters from a string in C++.
1. Using string::erase function
The standard solution to in-place erase a substring from a string is using the string::erase function. It modifies the string by deleting the specified range of characters. It takes one or two parameters: the position of the first character to be deleted, and optionally, the number of characters to be deleted. For example:
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#include <iostream> #include <string> void removeLastN(std::string &str, int n) { // no-const if (str.length() < n) { return ; } str.erase(str.length() - n); } int main() { std::string str = "C++20"; int n = 2; removeLastN(str, n); std::cout << str << ' '; // C++ return 0; } |
2. Using string::substr function
The substr() function is another function that can be used to remove the last n characters from a string. It returns a copy of a substring of the string, starting from a given position and having a given length. It takes one or two parameters: the position of the first character of the substring, and optionally, the length of the substring. Here’s an example of its usage:
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#include <iostream> #include <string> std::string removeLastN(std::string const &str, int n) { if (str.length() < n) { return str; } return str.substr(0, str.length() - n); } int main() { std::string str = "C++20"; int n = 2; str = removeLastN(str, n); std::cout << str << ' '; // C++ return 0; } |
Unlike string::erase function, the substr() function returns a new string, which preserves the original string and avoids side effects.
3. Using Regular Expressions
We can also use regular expressions to remove the last n characters from a string. To use regular expressions in C++, we need to import the <regex> header file and use its classes and functions. Here is an example:
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#include <iostream> #include <string> #include <regex> std::string removeLastN(std::string &str, int n) { if (str.length() < n) { return str; } // Create a regular expression pattern that matches any n characters // at the end of the string std::regex pattern(".{" + std::to_string(n) + "}$"); // Remove the last n characters from the string using regex_replace function // with an empty replacement return std::regex_replace(str, pattern, ""); } int main() { std::string str = "C++20"; int n = 2; str = removeLastN(str, n); std::cout << str << ' '; // C++ return 0; } |
That’s all about removing the last n characters from a string in C++.
Thanks for reading.
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