Operating Files larger than 2 GB in Linux

The key point is to add the-d_file_offset_bits = 64 Macro during compilation,ProgramIn, replace fseek and ftell with fseeko and ftello respectively.

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Man fseeko

Description

TheFseeko ()AndFtello ()Functions are identicalFseek ()AndFtell ()(SeeFseek(3), respectively, doesn't thatOffsetArgumentFseeko ()And the return valueFtello ()Is of TypeOff_tInsteadLong.

On ubuntures bothOff_tAndLongAre 32-bit types, but compilation

# DEFINE _ file_offset_bits 64

Will turnOff_tInto a 64-bit type.

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Compilation Method:

#! /Bin/sh

Arm-mv5sft-linux-gnueabi-gcc-d_file_offset_bits = 64 main. C-o Test

Gcc-d_file_offset_bits = 64 main. C-o x86test

Source program:

# Include <stdio. h>

# Include <sys/STAT. h>

# Include <sys/types. h>

# Include <unistd. h>

# Include <assert. h>

# Define FILENAME "10g. IMG"

# Define readbufsize 100

Int main ()

{

Printf ("sizeof (size_t) % d, sizeof (off_t) % d \ n", sizeof (size_t), sizeof (off_t ));

Struct stat Buf;

If (STAT (filename, & BUF )! = 0)

{

Perror ("stat :");

Return-1;
}

Printf ("% LLD \ n", Buf. st_size );

File * stream = fopen (filename, "RW ");

If (! Stream)

{

Perror ("fopen :");

Return-1;
}

Char readbuf [readbufsize];

{

Size_t ret = fread (readbuf, readbufsize, 1, stream );

Printf ("fread: % u \ n", RET );

Assert (ret = 1 );

}

Printf ("% LLD \ n", ftello (Stream ));

If (fseeko (stream,-100, seek_end )! = 0)

{

Perror ("fseeko :");

Return-1;
}

{

Size_t ret = fread (readbuf, readbufsize, 1, stream );

Printf ("fread: % u \ n", RET );

Assert (ret = 1 );

}

Printf ("% LLD \ n", ftello (Stream ));

Return 0;

}

 

Running result:

/Mnt/diska/partition1 #./test

Sizeof (size_t) 4, sizeof (off_t) 8

10485760000

Fread: 1

100

Fread: 1

10485760000