StackOverflow question

#include <iostream>
#include <fstream>

using namespace std;

// functions
bool file_exists(const char* f);

int main(int argc, char* argv[]){
    if(argc != 2){
        cerr << "Usage: fuzz \"file.jpg\"";
        return 0;
    }

    if(!file_exists(argv[1])){
        cerr << "Specified file doesn't exist.";
        return 1;
    }

    // Read source file
    FILE *fSource;
    fSource = fopen(argv[1], "r+");
    if(fSource == NULL){
        cerr << "Can't open file " << argv[1];
        return 2;
    }

    // Loop source file
    int byte;
    int i = 0;
    while((byte = fgetc(fSource)) != EOF){
        fseek(fSource, i++, SEEK_SET);
        fputc(byte ^ 0x13, fSource);
        fseek(fSource, i, SEEK_SET);
    }

    fclose(fSource);
    cout << "Fuzzed.";

    return 0;
}

bool file_exists(const char* f){
    ifstream file(f);
    return (bool) file;
}