Linux：使用libgen.h：basename，dirname

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Linux：使用libgen.h：basename，dirname

basename以及dirname是两个命令：

[test1280@localhost ~]$ which basename
/bin/basename
[test1280@localhost ~]$ which dirname
/bin/dirname

可以通过：

man 1 basename
man 1 dirname

来查看对应的帮助文档。

对于basename的描述是：

basename - strip directory and suffix from filenames
dirname - strip last component from file name

关于命令请大家自行阅读man手册。

basename以及dirname不仅是命令，而且还是函数，通过include头文件libgen.h即可使用。

Tips：
man 1 xxx 命令
man 2 xxx 系统级接口
man 3 xxx 函数库接口

使用下列man查看basename以及dirname函数：

man libgen.h
man 3 basename
man 3 dirname

basename, dirname - parse pathname components

The functions dirname() and basename() break a null-terminated pathname string into directory and filename components.
In the usual case, dirname() returns the string up to, but not including, the final '/', and basename() returns the component following the final '/'.  Trailing '/' characters are not counted  as  part of the pathname.

关键是下面这句话：

Both dirname() and basename() may modify the contents of path, so it may be desirable to pass a copy when calling one of these functions.

basename以及dirname都有可能修改字符串的内容，所以在调用他们时，尽可能传入一个副本，小心原始数据被破坏哦。

These functions may return pointers to statically allocated memory which may be overwritten by subsequent calls.

多次调用可能导致上一次内容被覆盖。

返回值：

Both dirname() and basename() return pointers to null-terminated strings.  (Do not pass these pointers to free(3).)

返回的都是以null结束的字符串。切记不要free。

两个函数都是Thread safety。

注意basename还有个兄弟版：

There are two different versions of basename() - the POSIX version described above, and the GNU version, which one gets after
#define _GNU_SOURCE
#include <string.h>
The  GNU  version  never modifies its argument, and returns the empty string when path has a trailing slash, and in particular also when it is "/".  There is no GNU version of dirname().

可不要想当然以为dirname也有兄弟。

附上测试代码：

测试环境：

CentOS 7:

[test1280@localhost ~]$ uname -a
Linux localhost.localdomain 3.10.0-327.el7.x86_64 #1 SMP Thu Nov 19 22:10:57 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
[test1280@localhost ~]$ g++ --version
g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

#include <iostream>
#include <stdlib.h>
#include <string.h>
#include <libgen.h>using namespace std;int main()
{char *dirc, *basec, *bname, *dname;const char *path[] = {"/usr/lib","/usr/","usr","/",".",".."};int i;for (i=0; i<6; i++){dirc = strdup(path[i]);basec = strdup(path[i]);dname = dirname(dirc);bname = basename(basec);cout<<">>>>>>"<<endl;cout<<"path:"<<path[i]<<endl;cout<<"dirname:"<<dname<<endl;cout<<"basename:"<<bname<<endl;cout<<"<<<<<<"<<endl<<endl;free(dirc);dirc = NULL;free(basec);basec = NULL;}return 0;
}

输出如下：

[test1280@localhost ~]$ ./main
>>>>>>
path:/usr/lib
dirname:/usr
basename:lib
<<<<<<>>>>>>
path:/usr/
dirname:/
basename:usr
<<<<<<>>>>>>
path:usr
dirname:.
basename:usr
<<<<<<>>>>>>
path:/
dirname:/
basename:/
<<<<<<>>>>>>
path:.
dirname:.
basename:.
<<<<<<>>>>>>
path:..
dirname:.
basename:..
<<<<<<

再多说一句，编译过程中遇到这么一个问题：

[test1280@localhost ~]$ g++ -o main main.C 
main.C: In function ‘int main()’:
main.C:17:2: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]};^
main.C:17:2: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
main.C:17:2: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
……

为啥有警告呢？原因在于一开始我是这么定义的：

        char *path[] = {"/usr/lib","/usr/","usr","/",".",".."};

没有加const修饰。

char 代表的意思是指向一个要被修改的字符串，而字面常量都是无法修改的，当然用char 来声明会有警告。

而使用const char *代表，指向一个“我永远不会修改的字符串”。

加上const，再编译就没有警告了。

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