How to find and replace string?

Question

If s is a std::string, then is there a function like the following?

s.replace("text to replace", "new text"); 

Answer 1

Replace first match

Use a combination of std::string::find and std::string::replace.

Find the first match:

std::string s; std::string toReplace("text to replace"); size_t pos = s.find(toReplace); 

Replace the first match:

s.replace(pos, toReplace.length(), "new text"); 

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A simple function for your convenience:

void replace_first(     std::string& s,     std::string const& toReplace,     std::string const& replaceWith ) {     std::size_t pos = s.find(toReplace);     if (pos == std::string::npos) return;     s.replace(pos, toReplace.length(), replaceWith); } 

Usage:

replace_first(s, "text to replace", "new text"); 

Demo.

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Replace all matches

Define this O(n) method using std::ostringstream as a buffer:

void replace_all(     std::string& s,     std::string const& toReplace,     std::string const& replaceWith ) {     std::ostringstream oss;     std::size_t pos = 0;     std::size_t prevPos = pos;      while (true) {         prevPos = pos;         pos = s.find(toReplace, pos);         if (pos == std::string::npos)             break;         oss << s.substr(prevPos, pos - prevPos);         oss << replaceWith;         pos += toReplace.size();     }      oss << s.substr(prevPos);     s = oss.str(); } 

Usage:

replace_all(s, "text to replace", "new text"); 

Demo.

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Boost

Alternatively, use boost::algorithm::replace_all:

#include <boost/algorithm/string.hpp> using boost::replace_all; 

Usage:

replace_all(s, "text to replace", "new text"); 

Answer 2

Do we really need a Boost library for seemingly such a simple task?

To replace all occurences of a substring use this function:

std::string ReplaceString(std::string subject, const std::string& search,                           const std::string& replace) {     size_t pos = 0;     while ((pos = subject.find(search, pos)) != std::string::npos) {          subject.replace(pos, search.length(), replace);          pos += replace.length();     }     return subject; } 

If you need performance, here is an optimized function that modifies the input string, it does not create a copy of the string:

void ReplaceStringInPlace(std::string& subject, const std::string& search,                           const std::string& replace) {     size_t pos = 0;     while ((pos = subject.find(search, pos)) != std::string::npos) {          subject.replace(pos, search.length(), replace);          pos += replace.length();     } } 

Tests:

std::string input = "abc abc def"; std::cout << "Input string: " << input << std::endl;  std::cout << "ReplaceString() return value: "            << ReplaceString(input, "bc", "!!") << std::endl; std::cout << "ReplaceString() input string not modified: "            << input << std::endl;  ReplaceStringInPlace(input, "bc", "??"); std::cout << "ReplaceStringInPlace() input string modified: "            << input << std::endl; 

Output:

Input string: abc abc def ReplaceString() return value: a!! a!! def ReplaceString() input string not modified: abc abc def ReplaceStringInPlace() input string modified: a?? a?? def