Simple cmmand line byte modifier that replaces raw bytes inside a given file

hexalter.cpp

#include <stdint.h>
#include <cstdio>
#include <cstdlib>
#include <vector>
#include <string>

using namespace std;

struct Patch
{
  uint32_t address;
  vector<uint8_t> values;
};

vector<Patch> entries;

void printUsage()
{
  printf("Usage: hexalter filename address1=byte1,..,byten ... addressn=byte1,...,byten\n");
}

bool parsePatch(const std::string& token)
{
  size_t equalIndex = token.find_first_of('=');
  
  if (equalIndex == string::npos)
    return false;
    
  Patch patch;
  patch.address = strtoul(token.substr(0, equalIndex).c_str(), NULL, 16);

  string values = token.substr(equalIndex+1);
  size_t startIndex = 0;
  size_t commaIndex;

  while ((commaIndex = values.find_first_of(',', startIndex)) != string::npos)
  {
    uint8_t value = strtoul(values.substr(startIndex, commaIndex).c_str(), NULL, 16);
    startIndex = commaIndex + 1;
    patch.values.push_back(value);
  }
  
  uint8_t value = strtoul(values.substr(startIndex).c_str(), NULL, 16);
  patch.values.push_back(value);
  
  entries.push_back(patch);
  
  return true;
}

int main(int argc, const char* argv[])
{
  if (argc < 3)
  {
    printUsage();
    return 1;
  }
  
  const char* filename = argv[1];
  
  for (int i = 2; i < argc; ++i)
  {
    if (!parsePatch(argv[i]))
    {
      printUsage();
      return 1;
    }
  }
  
  FILE* file = fopen(filename, "r+b");
  
  if (!file)
  {
    printf("Unable to open file. Exiting.\n");
    return 1;
  }
  
  fseek(file, 0L, SEEK_END);
  long fileSize = ftell(file);
  
  for (vector<Patch>::const_iterator it = entries.begin(); it != entries.end(); ++it)
  {
    const Patch& patch = *it;
    
    if (patch.address + patch.values.size() >= fileSize)
    {
      printf("Patch exceeds file size. Exiting.\n");
      break;
    }
    
    fseek(file, patch.address, SEEK_SET);
    fwrite(&patch.values[0], 1, patch.values.size(), file);
  }
  
  fclose(file);

  return 0;
}