Linux ftruncate函数

最新推荐文章于 2024-04-07 23:11:32 发布

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最新推荐文章于 2024-04-07 23:11:32 发布

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本文详细介绍了Linux系统中用于调整文件大小的两个关键函数：truncate和ftruncate。阐述了它们的功能、使用方法、参数需求及特性测试宏要求，深入分析了文件被截断时的行为变化，包括文件大小调整后的数据丢失或填充情况，以及函数在不同版本的glibc中的适应性。

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NAME
       truncate, ftruncate - truncate a file to a specified length

SYNOPSIS
       #include <unistd.h>
       #include <sys/types.h>

       int truncate(const char *path, off_t length);
       int ftruncate(int fd, off_t length);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       truncate():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

       ftruncate():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       The  truncate()  and ftruncate() functions cause the regular file named
       by path or referenced by fd to be truncated  to  a  size  of  precisely
       length bytes.

       If  the  file  previously  was larger than this size, the extra data is
       lost.  If the file previously was shorter,  it  is  extended,  and  the
       extended part reads as null bytes ('\0').

       The file offset is not changed.