(转)Linux：使用libgen.h：basename，dirname

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。