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  • 关于splice函数未定义

      没有用好man的下场呵呵,找个错误一直不知所措。

      先看splice函数:

     1 SPLICE(2)                  Linux Programmer's Manual                 SPLICE(2)
     2 
     3 NAME
     4        splice - splice data to/from a pipe
     5 
     6 SYNOPSIS
     7        #define _GNU_SOURCE         /* See feature_test_macros(7) */
     8        #include <fcntl.h>
     9 
    10        ssize_t splice(int fd_in, loff_t *off_in, int fd_out,
    11                       loff_t *off_out, size_t len, unsigned int flags);

    主要作用就是移动两个文件描述符中的数据,实现零拷贝操作。具体详见man或者google。

      说一下遇到的坑:看着书上知道它包含于fcntl头文件,可在编译的时候遇到了未知的未声明错误,找了半天百度终于找到答案。

    splice.c:48:53: error: ‘SPLICE_F_MORE’ undeclared (first use in this function)
    ret=splice(connfd,NULL,pipefd[1],NULL,32768,SPLICE_F_MORE|SPLICE_F_MOVE);
    ^
    splice.c:48:53: note: each undeclared identifier is reported only once for each function it appears in
    splice.c:48:67: error: ‘SPLICE_F_MOVE’ undeclared (first use in this function)
    ret=splice(connfd,NULL,pipefd[1],NULL,32768,SPLICE_F_MORE|SPLICE_F_MOVE);

      其实man里就可以看到还需要定义一个功能测试宏, _GNU_SOURCE,注意这里的顺序,小坑,不然依然编译不过。

      那么这个测试宏是干什么的呢,继续man下去:

    EATURE_TEST_MACROS(7)     Linux Programmer's Manual    FEATURE_TEST_MACROS(7)
    
    NAME
           feature_test_macros - feature test macros
    
    SYNOPSIS
           #include <features.h>
    
    DESCRIPTION
           Feature  test  macros  allow  the programmer to control the definitions
           that are exposed by system header files when a program is compiled.

      当程序被编译的时候,允许开发者控制被系统头文件所包含的宏。

      暂时也不明白,先就酱。

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  • 原文地址:https://www.cnblogs.com/manch1n/p/10533557.html
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