在文本文件中间附加字符串

Question

here is my code

#include <string>
#include <iostream>
#include <fstream>
int main(void){
    fstream myfile2;
    myfile2.open("test2.txt", ios::app);
    string checkline;
    getline(myfile2, checkline);
    int razmer=checkline.length();
    string balli="256";
    myfile2.seekp(razmer);
    myfile2<<balli;

}

test2.txt consists of 2 strings, so it is looks like

Ivanov
Petrov

I want to make from Ivanov -> Ivanov 256 . With no touching 2nd string. But my code did not work at all. Thanks in advance.

Answer 1

There's no easy way to edit a text file. The usual solution is to read the whole source file into memory, make your modifications in memory, and then write out all of the file.

In your example where the file seems to be line-based, you could read it line by line and put the lines in a std::vector . Edit the line you want to edit, then loop over the vector and write out the lines.

Note: When writing the file, you open it in write mode, so the file is recreated and looses all old contents.