linux下操縱大於2G檔案

要點是編譯時間候加-D_FILE_OFFSET_BITS=64宏，程式中把使用fseek,ftell的地方分別換成fseeko,ftello。

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man fseeko

DESCRIPTION

The fseeko() and ftello() functions are identical to fseek() and ftell() (see fseek(3)), respectively, except that the offset argument of fseeko() and the return value of ftello() is of type off_t instead of long.

On many architectures both off_t and long are 32-bit types, but compilation with

#define _FILE_OFFSET_BITS 64

will turn off_t into a 64-bit type.

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編譯方法：

#!/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

來源程式：

#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;

}

 

運行結果：

/mnt/DISKA/PARTITION1 # ./test

sizeof(size_t) 4, sizeof(off_t) 8

10485760000

fread:1

100

fread:1

10485760000