Replace part of a string with another string

Question

Is it possible in C++ to replace part of a string with another string?

Basically, I would like to do this:

QString string(\"hello $name\");
string.re         


        

Answer 1

If you want to do it quickly you can use a two scan approach. Pseudo code:

1. first parse. find how many matching chars.
2. expand the length of the string.
3. second parse. Start from the end of the string when we get a match we replace, else we just copy the chars from the first string.

I am not sure if this can be optimized to an in-place algo.

And a C++11 code example but I only search for one char.

#include 
#include 
#include 
using namespace std;

void ReplaceString(string& subject, char search, const string& replace)
{   
    size_t initSize = subject.size();
    int count = 0;
    for (auto c : subject) { 
        if (c == search) ++count;
    }

    size_t idx = subject.size()-1 + count * replace.size()-1;
    subject.resize(idx + 1, '\0');

    string reverseReplace{ replace };
    reverse(reverseReplace.begin(), reverseReplace.end());  

    char *end_ptr = &subject[initSize - 1];
    while (end_ptr >= &subject[0])
    {
        if (*end_ptr == search) {
            for (auto c : reverseReplace) {
                subject[idx - 1] = c;
                --idx;              
            }           
        }
        else {
            subject[idx - 1] = *end_ptr;
            --idx;
        }
        --end_ptr;
    }
}

int main()
{
    string s{ "Mr John Smith" };
    ReplaceString(s, ' ', "%20");
    cout << s << "\n";

}