获取文件大小：

int getFileLength(const char* fileName)
{
	int length = 0;
	FILE *file;
	file = fopen(fileName, "r");

	if (file == NULL)
	{
		return -1;
	}
	fseek(file, 0L, SEEK_END);
	length = ftell(file);

	fclose(file);

	return length;
}

已知文件大小读文件：

int getFileData(const char* fileName, unsigned char *data, int length)
{
	FILE *file;
	file = fopen(fileName, "r");

	if (file == NULL)
	{
		return -1;
	}

	int ret = fread(data, 1, length, file);

	fclose(file);

	return 0;
}

已知文件大小写文件：

int writeFile(const char* fileName, unsigned char *data, int size)
{
	FILE *file;
	file = fopen(fileName, "wb");

	if (file == NULL)
	{
		return -1;
	}

	int ret = fwrite(data, 1, size, file);

	fclose(file);

	return 0;
}