How to write in the same file C++ - c++

Question

I need to delete all the occurencies of a string in a file.
I receive the text as a string and erase every occurencies.
After I deleted all the occurencies i don't know how to save the string back to the file.
I've tried to close the file and wit ofstream to write in it but it didn't work.
#include <iostream>
#include <fstream>
#include <string>
int main () {
std::string file_contents = "";
std::ifstream myfile ("text.txt");
char ch;
if (myfile.is_open())
{
// READ FILE CONTENTS AS STRING
while ( myfile >> std::noskipws >> ch)
{
file_contents += ch;
}
// DISPLAY STRING
std::cout << file_contents << '\n';
// GET WORD TO BE DELETED
std::string word;
std::cout << "Please enter word to be deleted: ";
std::cin >> word;
std::string::size_type found;
std::string new_text;
//DELETE WORD FROM STRING
bool ok=0;
do{
found = file_contents.find(word);
ok=1;
if (found!=std::string::npos)
{
std::cout << word << " found at: " << found << '\n';
file_contents.erase(found, word.length());
std::cout << file_contents << '\n';
}
else
ok==0;
new_text=file_contents;
}while(ok==1);
myfile.close();
}
else std::cout << "Unable to open file";
return 0;
}

Answer 1

Okay so you must close ifstream instance before proceeding to write to the file again.
After closing the file, modify the content and then open the same file for write using ofstream and simply write the content.
#include <iostream>
#include <fstream>
#include <string>
int main() {
std::string file_contents = "";
std::ifstream myfile("text.txt");
char ch;
if (myfile.is_open())
{
// READ FILE CONTENTS AS STRING
while (myfile >> std::noskipws >> ch)
{
file_contents += ch;
}
myfile.close();
}
else {
std::cout << "Unable to open file";
return -1; // no need to continue if can't read it
}
// DISPLAY STRING
std::cout << file_contents << '\n';
// GET WORD TO BE DELETED
std::string word;
std::cout << "Please enter word to be deleted: ";
std::cin >> word;
//DELETE WORD FROM STRING
size_t found;
while ((found = file_contents.find(word)) != file_contents.npos)
{
std::cout << word << " found at: " << found << '\n';
file_contents.erase(found, word.length());
std::cout << file_contents << '\n';
}
// this will open in text mode and will replace all existing content
std::ofstream out("text.txt");
if (out.is_open()) {
out << file_contents;
out.close();
}
else {
std::cout << "Unable to open file for writing.\n";
return -2; // for failure to open for write
}
return 0;
}
Note: the loop you had went infinitely when I tried to execute it, I had to change it to the code shown above. Also, new_text is completely unnecessary, why have it?

Answer 2

The simpliest way is first to open as input stream. When finish open as output stream to write. It is not the only way you can do that.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main ()
{
std::string file_contents = "";
{
std::ifstream myfile ("text.txt");
if (! myfile.is_open())
{
else std::cout << "Unable to open file";
return 1;
}
// READ FILE CONTENTS AS STRING
char ch;
while ( myfile >> std::noskipws >> ch) file_contents += ch;
myfile.close();
}
{
std::string word;
std::cin >> word; // GET WORD TO BE DELETED
std::string::size_type found;
while((found = file_contents.find(word))!=std::string::npos)
file_contents.erase(found, word.length());
std::ofstream myfile ("text.txt");
myfile << file_contents<< std::flush;
myfile.close();
}
return 0;
}