How to read and write binary files? - Highscores

[DatFletch]

Hi,

Just wondering how to implement a highscore feature into a small game using binary. I have done it with txt before but want to try binary. I have been told that it is almost the same as txt so I did the following functions but it is unable to close down, so either unable to write to it or I made the binary file wrong or my code is completely wrong, any help would be appreciated, thanks

void Score::ReadScore()
{
	//Open the file for (r)eading
	FILE* pFile = fopen("HighScores.bin", "r");
	if (pFile != NULL)
	{
		char acWords[1024];
		fgets(acWords, 1024, pFile); //gets a string, max length 1024

		m_iHighScore = atoi(acWords);
	}
	fclose(pFile);
}

void Score::WriteScore()
{
	//Open the file for (r)eading
	FILE* pFile = fopen("HighScores.bin", "w+");
	if (pFile != NULL)
	{
		//char cLetter = fgetc(pFile); //get a character
		int iDisplayScore;

		if(m_iFroggerScore > m_iHighScore)
		{
			iDisplayScore = m_iFroggerScore;
		}
		else
		{
			iDisplayScore = m_iHighScore;
		}
		fprintf(pFile, "%d", iDisplayScore);
	}
	fclose(pFile);
}

[IceThatJaw]

I must ask, why aren't you using the C++ filestreams? Also you might want to look up bitsets to convert strings to binary.

[Lowest0ne]

About to say the same thing. If you're using member functions, you might as well use fstream.

As far as I've seen, the only reason to open a file in binary mode is if you need to read single characters where those characters might set the EOF bits on the istream.

The read()/write() functions still work with a non-binary open mode. They do read/write in binary as well. Read() and Write() expect char*, but you can cast your data types. Also note that data in a struct/class is stored contiguously, making this a very easy way to write and read data.

#include <iostream>
#include <fstream>
#include <string.h>

struct Data
{
  char word[64];
  int i;
  float f;
};


void print(void);
void read(void);


int main(void)
{  
  print();
  read();  
  return 0;
}

void print(void)
{
  Data myData;
  strcpy(myData.word, "Hello World");
  myData.i = 123;
  myData.f = 3.14159;
  
  // Can be opened in non-binary mode
  std::ofstream output("file.txt");
  output.write(reinterpret_cast<char*>(&myData), sizeof(myData));
  output.close();
}
void read(void)
{
  Data myData;

  // This is opened in binary mode, but it didn't have to be
  std::ifstream input("file.txt", std::ios::in | std::ios::binary);
  input.read(reinterpret_cast<char*>(&myData), sizeof(myData));
  std::cout << "Words: " << myData.word << '\n'
      << "Int  : " << myData.i << '\n'
      << "Float: " << myData.f << '\n';
  input.close();
}

It gets tricky though. If the class/struct had a pointer variable, then these functions will only read/write the pointer's value (not the data in the whatever it points to).