C ++快速读取较大文件的最佳方法

Question

During runtime I frequently need to read small portions of larger file (300 mb). Currently I always open up the file, read from it and then close it again like that:

FILE *file =fopen(szFileName,"rb");
if (file)
{
    fseek( file,iFirstByteToRead, SEEK_SET);
    fread(nEncodedBytes,sizeof(unsigned char), iLenCompressedBytes, file);
    fclose(file);
}

But that is too slow because I do that so frequently. Also I am not sure if fread could be sped up.

What is the best practice for such a situation, please?

Answer 1

Keep the file open and you'll do much better.

Try mmap for improved performance still.

Answer 2

The work related to file control always causes expensive cost. If you control several times for manage the file, you don't have to close file pointer.

Like below, once you get the file pointer,

FILE *stream = fopen(stream, “rb”);

if (stream != NULL)

You have to close stream file pointer after finishing in your program, and also if you have to manage a number of files, you would use a thread, which is dedicated as a file reading.