Append to text file

#include <fstream>
	
	std::ofstream ofstream1(MyFilepath.c_str(), std::ios_base::app);				//Append to existing file if present

	ofstream1 << "Hello";
	ofstream1.close();

Overwrite A Text File

#include <fstream>

//****************************************
//****************************************
//********** CREATE A TEXT FILE **********
//****************************************
//****************************************
void create_some_text_file (void)
{

	//----- CREATE A COPY OF THE ORIGINAL FILE IF THIS IS THE FIRST TIME WE'RE DOING THIS -----
	struct stat sb;
	int result = stat("/etc/wpa_supplicant/wpa_supplicant-original.conf", &sb);
	if ((result != 0) || (sb.st_mode & S_IFDIR))
	{
		system("sudo cp /etc/wpa_supplicant/wpa_supplicant.conf /etc/wpa_supplicant/wpa_supplicant-original.conf");
	}
	
	//----- CREATE NEW VERSION OF THE FILE -----
	
	//You can use this if you want to use the contents of some existing file as part of the output:
	//	std::ifstream ifstream1("/etc/some_source_file.conf", std::ios_base::in);
	//Then just use this wherever you want to insert it:
	//	output_file << ifstream1.rdbuf();
	
    std::ofstream output_file("/etc/wpa_supplicant/wpa_supplicant.conf");				//Will overwrite an existing file

	output_file << "# THIS FILE HAS BEEN AUTO GENERATED \n";
	output_file << "\n";
		
    output_file.close();
}