File reading

[mjbauer95]

What is the best way to read a file in C?
I have heard of using fread but then how do you find the size of the file?

This is my example code but it seems to have odd errors.

char * read(char * filename){
	FILE * fo;

	fo = fopen(filename, "r");
	if(fo){
		char * buffer = NULL;
		size_t result;
		int length;
		length = file_length(fo);
		result = fread(buffer,1,length,fo);
		fclose(fo);
		return buffer;
	} else {
		fclose(fo);
		return NULL;
	}
}

[l034n]

Well, it does indeed have errors. Check out this one.

unsigned char* ReadFile(const char* szFileName, long& length);

int main(int argc, char* argv[])
{
	long len = 0;
	const char* filename = "c:\\test.txt";
	unsigned char* buffer = ReadFile(filename, len);

	if(buffer)
	{
		// Do something with the buffer
		//.....

		// And clean up after yourself
		delete[] buffer;
		buffer = NULL;
	}

	return 0;
}

unsigned char* ReadFile(const char* szFileName, long& length)
{
	length = 0;
	unsigned char* buffer = NULL;
	FILE* fo = fopen(szFileName, "r");

	if(fo)
	{
		fseek(fo, 0, SEEK_END);
		length = ftell(fo);
		fseek(fo, 0, SEEK_SET);

		if(length)
		{
			buffer = new unsigned char[length];
			fread(buffer, length, 1, fo);
		}

		fclose(fo);
	}

	return buffer;
}

You may also consider using the *_s fuctions (like fopen_s).

Cheers

[weaknessforcats]

You should be able to seek to the end of the file (SEEK_END) and then do a tell to get the offset from the beginning.

[Banfa]

As long as you opened the file in binary mode, if you opened it in text mode then that is not a reliable method of getting the file size.

[mjbauer95]

Does the buffer have to be unsigned char * ?
Can it be const char * ?

I am new to C, sorry.

[l034n]

Yes, it can be a const char* if you don't want to modify it. So, the line:

unsigned char* buffer = ReadFile(filename, len);

would be:

const unsigned char* buffer = ReadFile(filename, len);

And also change the return value of ReadFile(). I wrote it as unsigned char* again because it was how i did it in the first example. But if you want to use char* instead of unsigned char* it doesn't matter, since they are of the same size (1 byte), just interpreted differently. However, i don't know why do you want to use a char*. The manipulation of bytes is better with unsigned char, hence BYTE is defined as unsigned char.