blocks|key|805593|text|您可以使用迭代器。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|805594|typedef+std::map<std::string,+std::map<std::string,+std::string>>::iterator+it_type;
for(it_type+iterator+=+m.begin();+iterator+!=+m.end();+iterator%2B%2B)+{
++++//+iterator->first+=+key
++++//+iterator->second+=+value
++++//+Repeat+if+you+also+want+to+iterate+through+the+second+map.
}|code-block|syntax|javascript|805595|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|$]]

You can use an iterator.

<pre><code>typedef std::map&lt;std::string, std::map&lt;std::string, std::string&gt;&gt;::iterator it_type;
for(it_type iterator = m.begin(); iterator != m.end(); iterator++) {
 // iterator-&gt;first = key
 // iterator-&gt;second = value
 // Repeat if you also want to iterate through the second map.
}
</code></pre>

blocks|key|805614|text|for(std::map<std::string,+std::map<std::string,+std::string>+>::iterator+outer_iter=map.begin();+outer_iter!=map.end();+%2B%2Bouter_iter)+{
++++for(std::map<std::string,+std::string>::iterator+inner_iter=outer_iter->second.begin();+inner_iter!=outer_iter->second.end();+%2B%2Binner_iter)+{
++++++++std::cout+<<+inner_iter->second+<<+std::endl;
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|805615|或者在C%2B%2B0x中更好：|unstyled|805616|for(auto+outer_iter=map.begin();+outer_iter!=map.end();+%2B%2Bouter_iter)+{
++++for(auto+inner_iter=outer_iter->second.begin();+inner_iter!=outer_iter->second.end();+%2B%2Binner_iter)+{
++++++++std::cout+<<+inner_iter->second+<<+std::endl;
++++}
}|805617|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>for(std::map&lt;std::string, std::map&lt;std::string, std::string&gt; &gt;::iterator outer_iter=map.begin(); outer_iter!=map.end(); ++outer_iter) {
 for(std::map&lt;std::string, std::string&gt;::iterator inner_iter=outer_iter-&gt;second.begin(); inner_iter!=outer_iter-&gt;second.end(); ++inner_iter) {
 std::cout &lt;&lt; inner_iter-&gt;second &lt;&lt; std::endl;
 }
}
</code></pre>

or nicer in C++0x:

<pre><code>for(auto outer_iter=map.begin(); outer_iter!=map.end(); ++outer_iter) {
 for(auto inner_iter=outer_iter-&gt;second.begin(); inner_iter!=outer_iter-&gt;second.end(); ++inner_iter) {
 std::cout &lt;&lt; inner_iter-&gt;second &lt;&lt; std::endl;
 }
}
</code></pre>

blocks|key|1020260|text|这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1020261|typedef+std::map<std::string,+std::string>+InnerMap;
typedef+std::map<std::string,+InnerMap>+OuterMap;

Outermap+mm;

...//set+the+initial+values

for+(OuterMap::iterator+i+=+mm.begin();+i+!=+mm.end();+%2B%2Bi)+{
++++InnerMap+&im+=+i->second;
++++for+(InnerMap::iterator+ii+=+im.begin();+ii+!=+im.end();+%2B%2Bii)+{
++++++++std::cout+<<+"map["+
++++++++++++++++++<<+i->first+
++++++++++++++++++<<+"]["+
++++++++++++++++++<<+ii->first+
++++++++++++++++++<<+"]+="+
++++++++++++++++++<<+ii->second+
++++++++++++++++++<<+'\n';
++++}
}+++|code-block|syntax|javascript|1020262|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|$]]

Do something like this:

<pre><code>typedef std::map&lt;std::string, std::string&gt; InnerMap;
typedef std::map&lt;std::string, InnerMap&gt; OuterMap;

Outermap mm;

...//set the initial values

for (OuterMap::iterator i = mm.begin(); i != mm.end(); ++i) {
 InnerMap &amp;im = i-&gt;second;
 for (InnerMap::iterator ii = im.begin(); ii != im.end(); ++ii) {
 std::cout &lt;&lt; "map[" 
 &lt;&lt; i-&gt;first 
 &lt;&lt; "][" 
 &lt;&lt; ii-&gt;first 
 &lt;&lt; "] =" 
 &lt;&lt; ii-&gt;second 
 &lt;&lt; '\n';
 }
} 
</code></pre>

blocks|key|805656|text|老问题，但剩下的答案在C%2B%2B11中已经过时了-您可以使用ranged+based+for+loop并简单地执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|805657|std::map<std::string,+std::map<std::string,+std::string>>+mymap;

for(auto+const+&ent1+:+mymap)+{
++//+ent1.first+is+the+first+key
++for(auto+const+&ent2+:+ent1.second)+{
++++//+ent2.first+is+the+second+key
++++//+ent2.second+is+the+data
++}
}|code-block|syntax|javascript|805658|这应该比以前的版本干净得多，并避免不必要的副本。|805659|一些人倾向于用引用变量的显式定义来替换注释(如果不使用，这些变量会被优化掉)：|805660|for(auto+const+&ent1+:+mymap)+{
++auto+const+&outer_key+=+ent1.first;
++auto+const+&inner_map+=+ent1.second;
++for(auto+const+&ent2+:+inner_map)+{
++++auto+const+&inner_key+++=+ent2.first;
++++auto+const+&inner_value+=+ent2.second;
++}
}|805661|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/language/range-for^0|S|L|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|C|$]]|$1|M|3|N|5|F|7|13|8|@]|9|@]|C|$G|H]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

Old question but the remaining answers are outdated as of C++11 - you can use a <a href="http://en.cppreference.com/w/cpp/language/range-for" rel="noreferrer">ranged based for loop</a> and simply do:

<pre><code>std::map&lt;std::string, std::map&lt;std::string, std::string&gt;&gt; mymap;

for(auto const &amp;ent1 : mymap) {
 // ent1.first is the first key
 for(auto const &amp;ent2 : ent1.second) {
 // ent2.first is the second key
 // ent2.second is the data
 }
}
</code></pre>

this should be much cleaner than the earlier versions, and avoids unnecessary copies. 

Some favour replacing the comments with explicit definitions of reference variables (which get optimised away if unused):

<pre><code>for(auto const &amp;ent1 : mymap) {
 auto const &amp;outer_key = ent1.first;
 auto const &amp;inner_map = ent1.second;
 for(auto const &amp;ent2 : inner_map) {
 auto const &amp;inner_key = ent2.first;
 auto const &amp;inner_value = ent2.second;
 }
}
</code></pre>

blocks|key|805682|text|当映射为常量时使用std::map<+std::string,+std::map<std::string,+std::string>+>::const_iterator。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|805683|entityMap^0|9|23|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

use <code>std::map&lt; std::string, std::map&lt;std::string, std::string&gt; &gt;::const_iterator</code> when map is const.

blocks|key|805692|text|C%2B%2B11：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|805693|std::map<+std::string,+std::map<std::string,+std::string>+>+m;
m["name1"]["value1"]+=+"data1";
m["name1"]["value2"]+=+"data2";
m["name2"]["value1"]+=+"data1";
m["name2"]["value2"]+=+"data2";
m["name3"]["value1"]+=+"data1";
m["name3"]["value2"]+=+"data2";

for+(auto+i+:+m)
++++for+(auto+j+:+i.second)
++++++++cout+<<+i.first.c_str()+<<+":"+<<+j.first.c_str()+<<+":"+<<+j.second.c_str()+<<+endl;|code-block|syntax|javascript|805694|输出：|805695|name1:value1:data1
name1:value2:data2
name2:value1:data1
name2:value2:data2
name3:value1:data1
name3:value2:data2|805696|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

C++11:

<pre><code>std::map&lt; std::string, std::map&lt;std::string, std::string&gt; &gt; m;
m["name1"]["value1"] = "data1";
m["name1"]["value2"] = "data2";
m["name2"]["value1"] = "data1";
m["name2"]["value2"] = "data2";
m["name3"]["value1"] = "data1";
m["name3"]["value2"] = "data2";

for (auto i : m)
 for (auto j : i.second)
 cout &lt;&lt; i.first.c_str() &lt;&lt; ":" &lt;&lt; j.first.c_str() &lt;&lt; ":" &lt;&lt; j.second.c_str() &lt;&lt; endl;
</code></pre>

output:

<pre><code>name1:value1:data1
name1:value2:data2
name2:value1:data1
name2:value2:data2
name3:value1:data1
name3:value2:data2
</code></pre>

blocks|key|805777|text|在C%2B%2B17+(或更高版本)中，您可以使用“结构化绑定”特性，该特性允许您使用单个元组/对定义具有不同名称的多个变量。示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|805778|for+(const+auto&+[name,+description]+:+planet_descriptions)+{
++++std::cout+<<+"Planet+"+<<+name+<<+":\n"+<<+description+<<+"\n\n";
}|code-block|syntax|javascript|805779|The+original+proposal+(由luminaries+Stroustrup，Herb+Sutter和Gabriel+Dos+Reis所著)读起来很有趣(建议的语法更直观)；还有proposed+wording+for+the+standard，它读起来很无聊，但更接近实际内容。|offset|length|805780|entityMap|0|LINK|mutability|MUTABLE|url|http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0144r0.pdf|1|http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0217r2.html^0|0|0|4|H|0|2O|X|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]|$I|10|J|11|1|12]]|A|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]|S|$5|N|O|P|A|$Q|T]]]]

With C++17 (or later), you can use the "structured bindings" feature, which lets you define multiple variables, with different names, using a single tuple/pair. Example:

<pre><code>for (const auto&amp; [name, description] : planet_descriptions) {
 std::cout &lt;&lt; "Planet " &lt;&lt; name &lt;&lt; ":\n" &lt;&lt; description &lt;&lt; "\n\n";
}
</code></pre>

The <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0144r0.pdf" rel="nofollow noreferrer">original proposal</a> (by luminaries Bjarne Stroustrup, Herb Sutter and Gabriel Dos Reis) is fun to read (and the suggested syntax is more intuitive IMHO); there's also the <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0217r2.html" rel="nofollow noreferrer">proposed wording for the standard</a> which is boring to read but is closer to what will actually go in.

How can I loop through a <code>std::map</code> in C++? My map is defined as:

<pre><code>std::map&lt; std::string, std::map&lt;std::string, std::string&gt; &gt;
</code></pre>

For example, the above container holds data like this:

<pre><code>m["name1"]["value1"] = "data1";
m["name1"]["value2"] = "data2";
m["name2"]["value1"] = "data1";
m["name2"]["value2"] = "data2";
m["name3"]["value1"] = "data1";
m["name3"]["value2"] = "data2";
</code></pre>

How can I loop through this map and access the various values?

How can I loop through a C++ map of maps?

容器

如何在C++中遍历std::map？我的地图定义为：std::map< std::string, std::map<std::string, std::string> >例如，上面的容器保存的数据如下：m["name1"]["value1"] = "data1";m["name1"]["value2"] = "data...

问如何遍历地图的C++地图？
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