blocks|key|1770475|text|_splitpath,+_wsplitpath,+_splitpath_s,+_wsplitpath_w|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1770476|这仅限于Windows+(Platform+SDK)|unstyled|1770477|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>_splitpath, _wsplitpath, _splitpath_s, _wsplitpath_w
</code></pre>

This is Windows (Platform SDK) only

blocks|key|1555449|text|最好的方法是不编写任何这样做的代码，而是调用现有的方法。在windows中，PathFindExtension方法可能是最简单的。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1555450|那么你为什么不自己写呢？|1555451|那么，以strrchr为例，当您对以下字符串"c:\program+files\AppleGate.Net\readme“使用该方法时会发生什么？".Net\readme“是扩展名吗？编写适用于少数示例用例的代码很容易，但编写适用于所有示例用例的代码可能要难得多。|1555452|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/bb773587(VS.85).aspx^0|12|H|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]]]

The best way is to not write any code that does it but call existing methods. In windows, the <a href="http://msdn.microsoft.com/en-us/library/bb773587(VS.85).aspx" rel="noreferrer" title="PathFindExtension">PathFindExtension</a> method is probably the simplest.

So why would you not write your own?

Well, take the strrchr example, what happens when you use that method on the following string "c:\program files\AppleGate.Net\readme"? Is ".Net\readme" the extension? It is easy to write something that works for a few example cases, but can be much harder to write something that works for all cases.

blocks|key|1770569|text|这是不是太简单了？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770570|#include+<iostream>
#include+<string>

int+main()
{
++std::string+fn+=+"filename.conf";
++if(fn.substr(fn.find_last_of(".")+%2B+1)+==+"conf")+{
++++std::cout+<<+"Yes..."+<<+std::endl;
++}+else+{
++++std::cout+<<+"No..."+<<+std::endl;
++}
}|code-block|syntax|javascript|1770571|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Is this too simple of a solution?

<pre><code>#include &lt;iostream&gt;
#include &lt;string&gt;

int main()
{
 std::string fn = "filename.conf";
 if(fn.substr(fn.find_last_of(".") + 1) == "conf") {
 std::cout &lt;&lt; "Yes..." &lt;&lt; std::endl;
 } else {
 std::cout &lt;&lt; "No..." &lt;&lt; std::endl;
 }
}
</code></pre>

blocks|key|1770588|text|你必须确保你的文件名有一个以上的点。示例：strchr或find.无法正确处理c:\.directoryname\file.name.with.too.many.dots.ext|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1770589|我最喜欢的是具有扩展(路径)函数的boost+filesystem+library|1770590|entityMap|0|LINK|mutability|MUTABLE|url|http://www.boost.org/doc/libs/release/libs/filesystem/index.html^0|L|6|S|5|13|1E|0|H|O|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|H|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

You have to make sure you take care of file names with more then one dot. 
example: <code>c:\.directoryname\file.name.with.too.many.dots.ext</code> would not be handled correctly by <code>strchr</code> or <code>find.</code> 

My favorite would be the <a href="http://www.boost.org/doc/libs/release/libs/filesystem/index.html" rel="noreferrer">boost filesystem library</a> that have an extension(path) function

blocks|key|1555605|text|使用std：：string的find/rfind解决了这个问题，但是如果您经常使用路径，那么您应该考虑使用boost::filesystem::path，因为它将使您的代码比摆弄原始字符串索引/迭代器干净得多。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1555606|我建议boost，因为它是一个高质量的，经过良好测试的，(开源和商业的)免费和完全可移植的库。|1555607|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Using std::string's find/rfind solves THIS problem, but if you work a lot with paths then you should look at boost::filesystem::path since it will make your code much cleaner than fiddling with raw string indexes/iterators.

I suggest boost since it's a high quality, well tested, (open source and commercially) free and fully portable library.

blocks|key|1770742|text|实际上，STL不需要太多代码就可以做到这一点，我建议你学习一些关于STL的知识，因为它让你可以做一些奇特的事情，不管怎样，这就是我使用的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770743|std::string+GetFileExtension(const+std::string&+FileName)
{
++++if(FileName.find_last_of(".")+!=+std::string::npos)
++++++++return+FileName.substr(FileName.find_last_of(".")%2B1);
++++return+"";
}|code-block|syntax|javascript|1770744|此解决方案将始终返回扩展名，即使是在"this.a.b.c.d.e.s.mp3“这样的字符串上，如果它找不到将返回的扩展名"”。|1770745|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

actually the STL can do this without much code, I advise you learn a bit about the STL because it lets you do some fancy things, anyways this is what I use.

<pre><code>std::string GetFileExtension(const std::string&amp; FileName)
{
 if(FileName.find_last_of(".") != std::string::npos)
 return FileName.substr(FileName.find_last_of(".")+1);
 return "";
}
</code></pre>

this solution will always return the extension even on strings like "this.a.b.c.d.e.s.mp3" if it cannot find the extension it will return "".

blocks|key|1770784|text|对于char数组类型的字符串，您可以使用以下命令：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770785|#include+<ctype.h>
#include+<string.h>

int+main()
{
++++char+filename[]+=+"apples.bmp";
++++char+extension[]+=+".jpeg";

++++if(compare_extension(filename,+extension)+==+true)
++++{
++++++++//+.....
++++}+else+{
++++++++//+.....
++++}

++++return+0;
}

bool+compare_extension(char+*filename,+char+*extension)
{
++++/*+Sanity+checks+*/

++++if(filename+==+NULL+%7C%7C+extension+==+NULL)
++++++++return+false;

++++if(strlen(filename)+==+0+%7C%7C+strlen(extension)+==+0)
++++++++return+false;

++++if(strchr(filename,+'.')+==+NULL+%7C%7C+strchr(extension,+'.')+==+NULL)
++++++++return+false;

++++/*+Iterate+backwards+through+respective+strings+and+compare+each+char+one+at+a+time+*/

++++for(int+i+=+0;+i+<+strlen(filename);+i%2B%2B)
++++{
++++++++if(tolower(filename[strlen(filename)+-+i+-+1])+==+tolower(extension[strlen(extension)+-+i+-+1]))
++++++++{
++++++++++++if(i+==+strlen(extension)+-+1)
++++++++++++++++return+true;
++++++++}+else
++++++++++++break;
++++}

++++return+false;
}|code-block|syntax|javascript|1770786|除了文件名之外，还可以处理文件路径。适用于C和C%2B%2B。和跨平台。|1770787|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For char array-type strings you can use this:

<pre><code>#include &lt;ctype.h&gt;
#include &lt;string.h&gt;

int main()
{
 char filename[] = "apples.bmp";
 char extension[] = ".jpeg";

 if(compare_extension(filename, extension) == true)
 {
 // .....
 } else {
 // .....
 }

 return 0;
}

bool compare_extension(char *filename, char *extension)
{
 /* Sanity checks */

 if(filename == NULL || extension == NULL)
 return false;

 if(strlen(filename) == 0 || strlen(extension) == 0)
 return false;

 if(strchr(filename, '.') == NULL || strchr(extension, '.') == NULL)
 return false;

 /* Iterate backwards through respective strings and compare each char one at a time */

 for(int i = 0; i &lt; strlen(filename); i++)
 {
 if(tolower(filename[strlen(filename) - i - 1]) == tolower(extension[strlen(extension) - i - 1]))
 {
 if(i == strlen(extension) - 1)
 return true;
 } else
 break;
 }

 return false;
}
</code></pre>

Can handle file paths in addition to filenames. Works with both C and C++. And cross-platform.

blocks|key|1555751|text|使用System::String的NET/CLI版本|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1555752|+++System::String%5E+GetFileExtension(System::String%5E+FileName)
+++{
+++++++int+Ext=FileName->LastIndexOf('.');
+++++++if(+Ext+!=+-1+)
+++++++++++return+FileName->Substring(Ext%2B1);
+++++++return+"";
+++}|code-block|syntax|javascript|1555753|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

A NET/CLI version using System::String

<pre><code> System::String^ GetFileExtension(System::String^ FileName)
 {
 int Ext=FileName-&gt;LastIndexOf('.');
 if( Ext != -1 )
 return FileName-&gt;Substring(Ext+1);
 return "";
 }
</code></pre>

blocks|key|1770846|text|尝试使用strstr|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1770847|char*+lastSlash;
lastSlash+=+strstr(filename,+".");|code-block|syntax|javascript|1770848|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cplusplus.com/reference/clibrary/cstring/strstr/^0|4|6|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Try to use <a href="http://www.cplusplus.com/reference/clibrary/cstring/strstr/" rel="nofollow">strstr</a>

<pre><code>char* lastSlash;
lastSlash = strstr(filename, ".");
</code></pre>

blocks|key|1555809|text|其他人提到了boost，但我只想添加实际的代码来实现这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1555810|#include+<boost/filesystem.hpp>
using+std::string;
string+texture+++++++++=+foo->GetTextureFilename();
string+file_extension++=+boost::filesystem::extension(texture);
cout+<<+"attempting+load+texture+named+"+<<+texture
+++++<<+"++++whose+extensions+seems+to+be+"+
+++++<<+file_extension+<<+endl;
//+Use+JPEG+or+PNG+loader+function,+or+report+invalid+extension|code-block|syntax|javascript|1555811|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Someone else mentioned boost but I just wanted to add the actual code to do this:

<pre><code>#include &lt;boost/filesystem.hpp&gt;
using std::string;
string texture = foo-&gt;GetTextureFilename();
string file_extension = boost::filesystem::extension(texture);
cout &lt;&lt; "attempting load texture named " &lt;&lt; texture
 &lt;&lt; " whose extensions seems to be " 
 &lt;&lt; file_extension &lt;&lt; endl;
// Use JPEG or PNG loader function, or report invalid extension
</code></pre>

blocks|key|1770931|text|今天我自己偶然发现了这个问题，尽管我已经有了一个可以工作的代码，但我发现它在某些情况下不能工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770932|虽然有些人已经建议使用一些外部库，但我更喜欢编写自己的代码来学习。|1770933|一些答案包括我最初使用的方法(查找最后一个".")，但我记得在linux上隐藏文件/文件夹以".“开头。因此，如果文件文件是隐藏的，并且没有扩展名，则将采用整个文件名作为扩展名。为了避免这种情况，我写了这段代码：|1770934|bool+getFileExtension(const+char+*+dir_separator,+const+std::string+&+file,+std::string+&+ext)
{
++++std::size_t+ext_pos+=+file.rfind(".");
++++std::size_t+dir_pos+=+file.rfind(dir_separator);

++++if(ext_pos>dir_pos%2B1)
++++{
++++++++ext.append(file.begin()%2Bext_pos,file.end());
++++++++return+true;
++++}

++++return+false;
}|code-block|syntax|javascript|1770935|我还没有完全测试这一点，但我认为它应该可以工作。|1770936|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|R|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I've stumbled onto this question today myself, even though I already had a working code I figured out that it wouldn't work in some cases.

While some people already suggested using some external libraries, I prefer to write my own code for learning purposes.

Some answers included the method I was using in the first place (looking for the last "."), but I remembered that on linux hidden files/folders start with ".".
So if file file is hidden and has no extension, the whole file name would be taken for extension.
To avoid that I wrote this piece of code:

<pre><code>bool getFileExtension(const char * dir_separator, const std::string &amp; file, std::string &amp; ext)
{
 std::size_t ext_pos = file.rfind(".");
 std::size_t dir_pos = file.rfind(dir_separator);

 if(ext_pos&gt;dir_pos+1)
 {
 ext.append(file.begin()+ext_pos,file.end());
 return true;
 }

 return false;
}
</code></pre>

I haven't tested this fully, but I think that it should work.

blocks|key|1770976|text|实际上，最简单的方法是|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1770977|char*+ext;
ext+=+strrchr(filename,'.')+|code-block|syntax|javascript|1770978|要记住的一件事是:如果文件名中不存在'.'，则ext将为NULL。|offset|length|style|CODE|1770979|entityMap^0|0|0|I|3|S|4|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

Actually, the easiest way is 

<pre><code>char* ext;
ext = strrchr(filename,'.') 
</code></pre>

One thing to remember: if <code>'.'</code> doesn't exist in filename, ext will be <code>NULL</code>.

blocks|key|1771016|text|或者，您可以使用以下命令：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1771017|++++char+*ExtractFileExt(char+*FileName)
++++{
++++++++std::string+s+=+FileName;
++++++++int+Len+=+s.length();
++++++++while(TRUE)
++++++++{
++++++++++++if(FileName[Len]+!=+'.')
++++++++++++++++Len--;
++++++++++++else
++++++++++++{
++++++++++++++++char+*Ext+=+new+char[s.length()-Len%2B1];
++++++++++++++++for(int+a=0;+a<s.length()-Len;+a%2B%2B)
++++++++++++++++++++Ext[a]+=+FileName[s.length()-(s.length()-Len)%2Ba];
++++++++++++++++Ext[s.length()-Len]+=+'\0';
++++++++++++++++return+Ext;
++++++++++++}
++++++++}
++++}|code-block|syntax|javascript|1771018|这段代码是跨平台的|1771019|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Or you can use this:

<pre><code> char *ExtractFileExt(char *FileName)
 {
 std::string s = FileName;
 int Len = s.length();
 while(TRUE)
 {
 if(FileName[Len] != '.')
 Len--;
 else
 {
 char *Ext = new char[s.length()-Len+1];
 for(int a=0; a&lt;s.length()-Len; a++)
 Ext[a] = FileName[s.length()-(s.length()-Len)+a];
 Ext[s.length()-Len] = '\0';
 return Ext;
 }
 }
 }
</code></pre>

This code is cross-platform

blocks|key|1555945|text|如果你使用Qt库，你可以试试QFileInfo的suffix()|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1555946|entityMap|0|LINK|mutability|MUTABLE|url|http://qt-project.org/doc/qt-4.8/qfileinfo.html|1|http://qt-project.org/doc/qt-4.8/qfileinfo.html#suffix^0|E|9|0|O|8|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

If you use Qt library, you can give a try to <a href="http://qt-project.org/doc/qt-4.8/qfileinfo.html" rel="nofollow">QFileInfo</a>'s <a href="http://qt-project.org/doc/qt-4.8/qfileinfo.html#suffix" rel="nofollow">suffix()</a>

blocks|key|1555999|text|下面是一个函数，它接受路径/文件名作为字符串，并将扩展名作为字符串返回。它完全是标准的c%2B%2B，并且应该在大多数平台上跨平台工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1556000|与这里的其他几个答案不同，它基于PathFindExtensions的文档处理windows的PathFindExtension处理的一些奇怪的情况。|1556001|wstring+get_file_extension(+wstring+filename+)
{
++++size_t+last_dot_offset+=+filename.rfind(L'.');
++++//+This+assumes+your+directory+separators+are+either+\+or+/
++++size_t+last_dirsep_offset+=+max(+filename.rfind(L'\\'),+filename.rfind(L'/')+);

++++//+no+dot+=+no+extension
++++if(+last_dot_offset+==+wstring::npos+)
++++++++return+L"";

++++//+directory+separator+after+last+dot+=+extension+of+directory,+not+file.
++++//+for+example,+given+C:\temp.old\file_that_has_no_extension+we+should+return+""+not+"old"
++++if(+(last_dirsep_offset+!=+wstring::npos)+&&+(last_dirsep_offset+>+last_dot_offset)+)
++++++++return+L"";

++++return+filename.substr(+last_dot_offset+%2B+1+);
}|code-block|syntax|javascript|1556002|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Here's a function that takes a path/filename as a string and returns the extension as a string. It is all standard c++, and should work cross-platform for most platforms.

Unlike several other answers here, it handles the odd cases that windows' PathFindExtension handles, based on PathFindExtensions's documentation.

<pre><code>wstring get_file_extension( wstring filename )
{
 size_t last_dot_offset = filename.rfind(L'.');
 // This assumes your directory separators are either \ or /
 size_t last_dirsep_offset = max( filename.rfind(L'\\'), filename.rfind(L'/') );

 // no dot = no extension
 if( last_dot_offset == wstring::npos )
 return L"";

 // directory separator after last dot = extension of directory, not file.
 // for example, given C:\temp.old\file_that_has_no_extension we should return "" not "old"
 if( (last_dirsep_offset != wstring::npos) &amp;&amp; (last_dirsep_offset &gt; last_dot_offset) )
 return L"";

 return filename.substr( last_dot_offset + 1 );
}
</code></pre>

blocks|key|1771142|text|我会选择boost::filesystem::extension+(带有C%2B%2B17的std::filesystem::path::extension)，但是如果你不能使用Boost，你只需要验证扩展，一个简单的解决方案是：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1771143|bool+ends_with(const+std::string+&filename,+const+std::string+&ext)
{
++return+ext.length()+<=+filename.length()+&&
+++++++++std::equal(ext.rbegin(),+ext.rend(),+filename.rbegin());
}

if+(ends_with(filename,+".conf"))
{+/*+...+*/+}|code-block|syntax|javascript|1771144|entityMap|0|LINK|mutability|MUTABLE|url|http://www.boost.org/doc/libs/1_58_0/libs/filesystem/doc/reference.html#path-extension|1|https://en.cppreference.com/w/cpp/filesystem/path/extension^0|4|S|16|W|4|S|0|16|W|1|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]|$9|12|A|13|1|14]]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]|S|$5|N|O|P|E|$Q|T]]]]

I'd go with <a href="http://www.boost.org/doc/libs/1_58_0/libs/filesystem/doc/reference.html#path-extension" rel="nofollow noreferrer"><code>boost::filesystem::extension</code></a> (<a href="https://en.cppreference.com/w/cpp/filesystem/path/extension" rel="nofollow noreferrer"><code>std::filesystem::path::extension</code></a> with C++17) but if you cannot use Boost and you just have to verify the extension, a simple solution is:

<pre><code>bool ends_with(const std::string &amp;filename, const std::string &amp;ext)
{
 return ext.length() &lt;= filename.length() &amp;&amp;
 std::equal(ext.rbegin(), ext.rend(), filename.rbegin());
}

if (ends_with(filename, ".conf"))
{ /* ... */ }
</code></pre>

blocks|key|1771181|text|这是我想出来的一个解决方案。然后，我注意到它类似于@serengeor发布的内容。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1771182|它适用于std::string和find_last_of，但如果修改为使用char数组和strrchr，其基本思想也将适用。它处理隐藏的文件，以及表示当前目录的额外的点。它是独立于平台的。|offset|length|style|CODE|1771183|string+PathGetExtension(+string+const+&+path+)
{
++string+ext;

++//+Find+the+last+dot,+if+any.
++size_t+dotIdx+=+path.find_last_of(+"."+);
++if+(+dotIdx+!=+string::npos+)
++{
++++//+Find+the+last+directory+separator,+if+any.
++++size_t+dirSepIdx+=+path.find_last_of(+"/\\"+);

++++//+If+the+dot+is+at+the+beginning+of+the+file+name,+do+not+treat+it+as+a+file+extension.
++++//+e.g.,+a+hidden+file:++".alpha".
++++//+This+test+also+incidentally+avoids+a+dot+that+is+really+a+current+directory+indicator.
++++//+e.g.:++"alpha/./bravo"
++++if+(+dotIdx+>+dirSepIdx+%2B+1+)
++++{
++++++ext+=+path.substr(+dotIdx+);
++++}
++}

++return+ext;
}|code-block|syntax|javascript|1771184|单元测试：|1771185|int+TestPathGetExtension(+void+)
{
++int+errCount+=+0;

++string+tests[][2]+=+
++{
++++{+"/alpha/bravo.txt",+".txt"+},
++++{+"/alpha/.bravo",+""+},
++++{+".alpha",+""+},
++++{+"./alpha.txt",+".txt"+},
++++{+"alpha/./bravo",+""+},
++++{+"alpha/./bravo.txt",+".txt"+},
++++{+"./alpha",+""+},
++++{+"c:\\alpha\\bravo.net\\charlie.txt",+".txt"+},
++};

++int+n+=+sizeof(+tests+)+/+sizeof(+tests[0]+);

++for+(+int+i+=+0;+i+<+n;+%2B%2Bi+)
++{
++++string+ext+=+PathGetExtension(+tests[i][0]+);
++++if+(+ext+!=+tests[i][1]+)
++++{
++++++%2B%2BerrCount;
++++}
++}

++return+errCount;
}|1771186|entityMap^0|0|4|B|G|C|11|4|18|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@$D|U|E|V|F|G]|$D|W|E|X|F|G]|$D|Y|E|Z|F|G]|$D|10|E|11|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|12|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|14|8|@]|9|@]|A|$K|L]]|$1|Q|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|R|$]]

This is a solution I came up with. Then, I noticed that it is similar to what @serengeor posted.

It works with <code>std::string</code> and <code>find_last_of</code>, but the basic idea will also work if modified to use <code>char</code> arrays and <code>strrchr</code>.
It handles hidden files, and extra dots representing the current directory. It is platform independent.

<pre><code>string PathGetExtension( string const &amp; path )
{
 string ext;

 // Find the last dot, if any.
 size_t dotIdx = path.find_last_of( "." );
 if ( dotIdx != string::npos )
 {
 // Find the last directory separator, if any.
 size_t dirSepIdx = path.find_last_of( "/\\" );

 // If the dot is at the beginning of the file name, do not treat it as a file extension.
 // e.g., a hidden file: ".alpha".
 // This test also incidentally avoids a dot that is really a current directory indicator.
 // e.g.: "alpha/./bravo"
 if ( dotIdx &gt; dirSepIdx + 1 )
 {
 ext = path.substr( dotIdx );
 }
 }

 return ext;
}
</code></pre>

Unit test:

<pre><code>int TestPathGetExtension( void )
{
 int errCount = 0;

 string tests[][2] = 
 {
 { "/alpha/bravo.txt", ".txt" },
 { "/alpha/.bravo", "" },
 { ".alpha", "" },
 { "./alpha.txt", ".txt" },
 { "alpha/./bravo", "" },
 { "alpha/./bravo.txt", ".txt" },
 { "./alpha", "" },
 { "c:\\alpha\\bravo.net\\charlie.txt", ".txt" },
 };

 int n = sizeof( tests ) / sizeof( tests[0] );

 for ( int i = 0; i &lt; n; ++i )
 {
 string ext = PathGetExtension( tests[i][0] );
 if ( ext != tests[i][1] )
 {
 ++errCount;
 }
 }

 return errCount;
}
</code></pre>

blocks|key|1556134|text|如果你碰巧使用了Poco库，你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1556135|#include+<Poco/Path.h>

...

std::string+fileExt+=+Poco::Path("/home/user/myFile.abc").getExtension();+//+==+"abc"|code-block|syntax|javascript|1556136|entityMap|0|LINK|mutability|MUTABLE|url|http://pocoproject.org/^0|8|4|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

If you happen to use <a href="http://pocoproject.org/" rel="nofollow">Poco</a> libraries you can do:

<pre><code>#include &lt;Poco/Path.h&gt;

...

std::string fileExt = Poco::Path("/home/user/myFile.abc").getExtension(); // == "abc"
</code></pre>

blocks|key|1771289|text|如果将扩展名视为最后一个点及其后面可能的字符，但前提是它们不包含目录分隔符，则以下函数将返回扩展名起始索引，如果找不到扩展名，则返回-1。当你有了它，你可以做任何你想做的事情，像剥离扩展，改变它，检查它等等。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1771290|long+get_extension_index(string+path,+char+dir_separator+=+'/')+{
++++//+Look+from+the+end+for+the+first+'.',
++++//+but+give+up+if+finding+a+dir+separator+char+first
++++for(long+i+=+path.length()+-+1;+i+>=+0;+--i)+{
++++++++if(path[i]+==+'.')+{
++++++++++++return+i;
++++++++}
++++++++if(path[i]+==+dir_separator)+{
++++++++++++return+-1;
++++++++}
++++}
++++return+-1;
}|code-block|syntax|javascript|1771291|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If you consider the extension as the last dot and the possible characters after it, but only if they don't contain the directory separator character, the following function returns the extension starting index, or -1 if no extension found. When you have that you can do what ever you want, like strip the extension, change it, check it etc.

<pre><code>long get_extension_index(string path, char dir_separator = '/') {
 // Look from the end for the first '.',
 // but give up if finding a dir separator char first
 for(long i = path.length() - 1; i &gt;= 0; --i) {
 if(path[i] == '.') {
 return i;
 }
 if(path[i] == dir_separator) {
 return -1;
 }
 }
 return -1;
}
</code></pre>

blocks|key|1771340|text|我使用了PathFindExtension()函数来判断它是否是一个有效的tif文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1771341|#include+<Shlwapi.h>
bool+A2iAWrapperUtility::isValidImageFile(string+imageFile)
{
++++char+*+pStrExtension+=+::PathFindExtension(imageFile.c_str());

++++if+(pStrExtension+!=+NULL+&&+strcmp(pStrExtension,+".tif")+==+0)
++++{
++++++++return+true;
++++}

++++return+false;
}|code-block|syntax|javascript|1771342|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I used PathFindExtension() function to know whether it is a valid tif file or not.

<pre><code>#include &lt;Shlwapi.h&gt;
bool A2iAWrapperUtility::isValidImageFile(string imageFile)
{
 char * pStrExtension = ::PathFindExtension(imageFile.c_str());

 if (pStrExtension != NULL &amp;&amp; strcmp(pStrExtension, ".tif") == 0)
 {
 return true;
 }

 return false;
}
</code></pre>

blocks|key|1556261|text|使用C%2B%2B17和它的std::filesystem::path::extension+(该库是boost：：filesystem的后继库)，您可以使您的语句比使用std::string更具表现力。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1556262|#include+<iostream>
#include+<filesystem>+//+C%2B%2B17
namespace+fs+=+std::filesystem;

int+main()
{
++++fs::path+filePath+=+"my/path/to/myFile.conf";
++++if+(filePath.extension()+==+".conf")+//+Heed+the+dot.
++++{
++++++++std::cout+<<+filePath.stem()+<<+"+is+a+valid+type.";+//+Output:+"myFile+is+a+valid+type."
++++}
++++else
++++{
++++++++std::cout+<<+filePath.filename()+<<+"+is+an+invalid+type.";+//+Output:+e.g.+"myFile.cfg+is+an+invalid+type"
++++}
}|code-block|syntax|javascript|1556263|另请参见std::filesystem::path::stem、std::filesystem::path::filename。|1556264|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/filesystem/path/extension|1|http://en.cppreference.com/w/cpp/filesystem/path/stem|2|http://en.cppreference.com/w/cpp/filesystem/path/filename^0|A|W|29|B|A|W|0|0|0|4|R|1|W|V|2|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|17|8|@]|D|@$9|18|A|19|1|1A]|$9|1B|A|1C|1|1D]]|E|$]]|$1|M|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]|W|$5|P|Q|R|E|$S|X]]]]

With C++17 and its <a href="http://en.cppreference.com/w/cpp/filesystem/path/extension" rel="noreferrer"><code>std::filesystem::path::extension</code></a> (the library is the successor to boost::filesystem) you would make your statement more expressive than using e.g. <code>std::string</code>.

<pre><code>#include &lt;iostream&gt;
#include &lt;filesystem&gt; // C++17
namespace fs = std::filesystem;

int main()
{
 fs::path filePath = "my/path/to/myFile.conf";
 if (filePath.extension() == ".conf") // Heed the dot.
 {
 std::cout &lt;&lt; filePath.stem() &lt;&lt; " is a valid type."; // Output: "myFile is a valid type."
 }
 else
 {
 std::cout &lt;&lt; filePath.filename() &lt;&lt; " is an invalid type."; // Output: e.g. "myFile.cfg is an invalid type"
 }
}
</code></pre>

See also <a href="http://en.cppreference.com/w/cpp/filesystem/path/stem" rel="noreferrer">std::filesystem::path::stem</a>, <a href="http://en.cppreference.com/w/cpp/filesystem/path/filename" rel="noreferrer">std::filesystem::path::filename</a>.

Given a string <code>"filename.conf"</code>, how to I verify the extension part?

I need a cross platform solution.

How to get file extension from string in C++

单元测试

Windows

给定一个字符串"filename.conf"，如何验证扩展部分？我需要一个跨平台的解决方案。

问如何在C++中从字符串中获取文件扩展名
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