1.编译含有splice()函数的程序时出现,'SPLICE_F_MOVE' undeclared,'SPLICE_F_NONBLOCK' ‘SPLICE_F_MORE' 也是一样undeclared!
2.使用man splice查看,发现要定义宏_GNU_SOURCE
1 #define _GNU_SOURCE /* See feature_test_macros(7) */2 #include <fcntl.h>3 4 ssize_t splice(int fd_in, loff_t *off_in, int fd_out, loff_t *off_out, size_t len, unsigned int flags);
我们跟着后面宏的注释See feature_test_macros(7)
1 $:man feature_test_macros
man手册上面的描述是:特性测试宏允许程序编译时控制系统头文件的宏定义!
1 NAME2 feature_test_macros - feature test macros3 4 SYNOPSIS5 #include <features.h>6 7 DESCRIPTION8 Feature test macros allow the programmer to control the definitions that are exposed by system header files when a program is compiled.
3.我们找找看,splice()函数的这个几个flags参数宏定义在哪里。splice()函数定义在<fcntl.h>头文件里面,查看头文件
1 $:vim /usr/include/fcntl.h
然而里面并没有这几个宏,但里面有包含了<features.h>,<bits/fcntl.h>文件,我们跟进去这2个文件。我的系统是64位的kail。
bits文件夹在/usr/include/x86_64-linux-gnu/bits/
1 $:vim /usr/include/features.h2 $:vim /usr/include/x86_64-linux-gnu/bits/fcntl.h
这2个里面都也没有,<bits/fcntl.h>文件里面又包含了<bits/fcntl-linux.h>。我们继续跟进。
1 $:vim /usr/include/x86_64-linux-gnu/bits/fcntl-linux.h
这次我们找到了:
1 /* Flags for SPLICE and VMSPLICE. */2 # define SPLICE_F_MOVE 1 /* Move pages instead of copying. */3 # define SPLICE_F_NONBLOCK 2 /* Don't block on the pipe splicing4 (but we may still block on the fd5 we splice from/to). */6 # define SPLICE_F_MORE 4 /* Expect more data. */7 # define SPLICE_F_GIFT 8 /* Pages passed in are a gift. */
4.现在我们根据这几个宏定义的上下文来查看跟_GNU_SOURCE宏的联系。
这4个宏包含在#ifdef __USE_GNU里面,我回头在看看features.h
1 $:vim /usr/include/features.h
直接搜索__USE_GNU,发现里面有这个定义,跟_GNU_SOURCE关联。
#ifdef _GNU_SOURCE# define __USE_GNU 1#endif
5.如果不注重里面的包含细节,直接用grep搜索,简单粗暴!!!
$:grep -rn 'SPLICE_F' /usr/include/
原标题:splice()函数,SPLICE_F_MOVE SPLICE_F_NONBLOCK SPLICE_F_MORE undeclared
关键词:函数