How can I trim whitespace from the beginning and end of a `std::string`?

Question

Ryan McCombe · Accepted Answer

Trimming whitespace from the beginning and end of a std::string is a common task in text processing. Here are several ways to achieve this in C++.

Using Custom Functions

For example:

1#include <iostream>
2#include <string>
3#include <algorithm>
4#include <cctype>
5
6std::string TrimWhitespace(const std::string& str) {
7  size_t first = str.find_first_not_of(' ');
8  size_t last = str.find_last_not_of(' ');
9  return str.substr(first, (last - first + 1));
10}
11
12int main() {
13  std::string Text{"   Hello, World!   "};
14
15  std::string Trimmed = TrimWhitespace(Text);  
16
17  std::cout << '"' << Trimmed << '"';
18}

1"Hello, World!"

Using `std::isspace`

You can also use std::isspace to handle all types of whitespace characters. For example:

1#include <iostream>
2#include <string>
3#include <algorithm>
4#include <cctype>
5
6std::string TrimWhitespace(const std::string& str) {
7  auto start = std::find_if_not(
8    str.begin(), str.end(), ::isspace
9  );  
10
11  auto end = std::find_if_not(
12    str.rbegin(), str.rend(), ::isspace
13  ).base();  
14
15  return (start < end) ? std::string(start, end)
16                       : std::string();
17}
18
19int main() {
20  std::string Text{"\t  Hello, World! \n"};
21  std::string Trimmed = TrimWhitespace(Text);  
22  std::cout << '"' << Trimmed << '"';
23}

1"Hello, World!"

Using Regular Expressions

If you prefer using regular expressions, you can use the <regex> library to trim whitespace. For example:

1#include <iostream>
2#include <string>
3#include <regex>
4
5std::string TrimWhitespace(const std::string& str) {
6  std::regex wsRegex("^\\s+|\\s+$");
7  return std::regex_replace(str, wsRegex, "");  
8}
9
10int main() {
11  std::string Text{"\t  Hello, World! \n"};
12
13  std::string Trimmed = TrimWhitespace(Text);  
14
15  std::cout << '"' << Trimmed << '"';
16}

1"Hello, World!"

Considerations

Efficiency: Custom functions are generally more efficient for simple whitespace trimming.
Flexibility: Using std::isspace ensures all whitespace characters are handled.
Complexity: Regular expressions can handle more complex patterns but may be slower.

By using these methods, you can effectively trim whitespace from the beginning and end of a std::string.

Manipulating `std::string` Objects

Trim Whitespace

Using Custom Functions

Using `std::isspace`

Using Regular Expressions

Considerations

Manipulating `std::string` Objects

Professional C++

Questions & Answers

Trim Whitespace

Using Custom Functions

Using std::isspace

Using Regular Expressions

Considerations

Manipulating std::string Objects

Questions & Answers

Using `std::isspace`

Manipulating `std::string` Objects