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

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

This gets the position:

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

And this replaces the first occurrence:

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

---

Now you can simply create a function for your convenience:

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

Answer 2

Here's the version I ended up writing that replaces all instances of the target string in a given string. Works on any string type.

template <typename T, typename U>
T &replace (
          T &str, 
    const U &from, 
    const U &to)
{
    size_t pos;
    size_t offset = 0;
    const size_t increment = to.size();

    while ((pos = str.find(from, offset)) != T::npos)
    {
        str.replace(pos, from.size(), to);
        offset = pos + increment;
    }

    return str;
}

Example:

auto foo = "this is a test"s;
replace(foo, "is"s, "wis"s);
cout << foo;

Output:

thwis wis a test

Note that even if the search string appears in the replacement string, this works correctly.

Answer 3

#include <iostream>
#include <string>
using namespace std;

int main ()
{
    string str("one three two four");
    string str2("three");
    str.replace(str.find(str2),str2.length(),"five");
    cout << str << endl;
    return 0;
}

Output

one five two four