Question

I am working on ubuntu. I have a file called test.txt. I would like to replace the second line with another line. How can I do that? I don’t want to create a new file and delete the first one.

I would like to specify that the lenght of the new line is the same with the length of the ond one

Answer 1

Try something like:

#include <fstream>
#include <string>

int main() {
    const int lineToReplace = 14;
    std::fstream file("myfile.txt", std::ios::in | std::ios::out);
    char line[255];
    for (int i=0; i<lineToReplace-1; ++i) 
        file.getline(line, 255); // This already skips the newline
    file.tellg();
    file << "Your contents here" << std::endl;
    file.close();
    return 0;
}

Note that line can hold up to 254 bytes (plus the null terminator), so if your line takes more than that, adjust accordingly.