blocks|key|1850466|text|看看sprintf()和他的家人。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1850467|entityMap^0|2|9|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|$]]

Take a look at <code>sprintf()</code> and family.

blocks|key|2064518|text|您也可以使用stringstream。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2064519|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cplusplus.com/reference/iostream/stringstream/^0|6|C|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You could also use <a href="http://www.cplusplus.com/reference/iostream/stringstream/" rel="nofollow noreferrer">stringstream</a>.

blocks|key|2064530|text|//+The+C+way:
char+buffer[32];
snprintf(buffer,+sizeof(buffer),+"%25g",+myDoubleVar);

//+The+C%2B%2B03+way:
std::ostringstream+sstream;
sstream+<<+myDoubleVar;
std::string+varAsString+=+sstream.str();

//+The+C%2B%2B11+way:
std::string+varAsString+=+std::to_string(myDoubleVar);

//+The+boost+way:
std::string+varAsString+=+boost::lexical_cast<std::string>(myDoubleVar);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2064531|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>// The C way:
char buffer[32];
snprintf(buffer, sizeof(buffer), "%g", myDoubleVar);

// The C++03 way:
std::ostringstream sstream;
sstream &lt;&lt; myDoubleVar;
std::string varAsString = sstream.str();

// The C++11 way:
std::string varAsString = std::to_string(myDoubleVar);

// The boost way:
std::string varAsString = boost::lexical_cast&lt;std::string&gt;(myDoubleVar);
</code></pre>

blocks|key|1850538|text|如果您使用C%2B%2B，请避免使用sprintf。它是非C%2B%2By的，有几个问题。Stringstreams是可选的方法，最好像Boost.LexicalCast中那样封装，这很容易做到：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1850539|template+<typename+T>
std::string+to_string(T+const&+value)+{
++++stringstream+sstr;
++++sstr+<<+value;
++++return+sstr.str();
}|code-block|syntax|javascript|1850540|用法：|1850541|string+s+=+to_string(42.5);|1850542|entityMap|0|LINK|mutability|MUTABLE|url|http://www.boost.org/doc/libs/1_37_0/libs/conversion/lexical_cast.htm^0|E|7|1O|H|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

If you use C++, avoid <code>sprintf</code>. It's un-C++y and has several problems. Stringstreams are the method of choice, preferably encapsulated as in <a href="http://www.boost.org/doc/libs/1_37_0/libs/conversion/lexical_cast.htm" rel="noreferrer">Boost.LexicalCast</a> which can be done quite easily:

<pre><code>template &lt;typename T&gt;
std::string to_string(T const&amp; value) {
 stringstream sstr;
 sstr &lt;&lt; value;
 return sstr.str();
}
</code></pre>

Usage:

<pre><code>string s = to_string(42.5);
</code></pre>

blocks|key|2064586|text|嘿，我只是写了这个(与这个问题无关)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2064587|string+temp+=+"";
stringstream+outStream;
double+ratio+=+(currentImage->width*1.0f)/currentImage->height;
outStream+<<+"+R:+"+<<+ratio;
temp+=+outStream.str();

/*+rest+of+the+code+*/|code-block|syntax|javascript|2064588|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|$]]

Heh, I just wrote this (unrelated to this question):

<pre><code>string temp = "";
stringstream outStream;
double ratio = (currentImage-&gt;width*1.0f)/currentImage-&gt;height;
outStream &lt;&lt; " R: " &lt;&lt; ratio;
temp = outStream.str();

/* rest of the code */
</code></pre>

blocks|key|1850944|text|sprintf是可以的，但在C%2B%2B中，使用stringstream进行转换更好、更安全，而且速度也稍慢|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1850945|#include+<sstream>
#include+<string>

//+In+some+function:
double+d+=+453.23;
std::ostringstream+os;
os+<<+d;
std::string+str+=+os.str();|code-block|syntax|javascript|1850946|您也可以使用Boost.LexicalCast|1850947|#include+<boost/lexical_cast.hpp>
#include+<string>

//+In+some+function:
double+d+=+453.23;
std::string+str+=+boost::lexical_cast<string>(d);|1850948|在这两种情况下，后面的str都应该是"453.23"。LexicalCast有一些优势，它可以确保转换是完整的。它在内部使用stringstream%25s。|1850949|entityMap|0|LINK|mutability|MUTABLE|url|http://www.boost.org/doc/libs/1_37_0/libs/conversion/lexical_cast.htm^0|0|7|L|C|0|0|6|H|0|0|0|B|3|I|8|1Q|C|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|D|@$9|15|A|16|1|17]]|E|$]]|$1|M|3|N|5|H|7|18|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

<code>sprintf</code> is okay, but in C++, the better, safer, and also slightly slower way of doing the conversion is with <code>stringstream</code>:

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

// In some function:
double d = 453.23;
std::ostringstream os;
os &lt;&lt; d;
std::string str = os.str();
</code></pre>

You can also use <a href="http://www.boost.org/doc/libs/1_37_0/libs/conversion/lexical_cast.htm" rel="noreferrer">Boost.LexicalCast</a>:

<pre><code>#include &lt;boost/lexical_cast.hpp&gt;
#include &lt;string&gt;

// In some function:
double d = 453.23;
std::string str = boost::lexical_cast&lt;string&gt;(d);
</code></pre>

In both instances, <code>str</code> should be <code>"453.23"</code> afterward. LexicalCast has some advantages in that it ensures the transformation is complete. It uses <code>stringstream</code>s internally.

blocks|key|2065071|text|Herb+Sutter有一个很棒的article+on+string+formatting。我推荐你去读一读。我已经linked+it+before+on+SO了。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2065072|entityMap|0|LINK|mutability|MUTABLE|url|http://www.gotw.ca/publications/mill19.htm|1|https://stackoverflow.com/questions/191757/c-concatenate-string-and-int#192242^0|H|S|0|1M|G|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]]]]

Herb Sutter has an excellent <a href="http://www.gotw.ca/publications/mill19.htm" rel="nofollow noreferrer">article on string formatting</a>. I recommend reading it. I've <a href="https://stackoverflow.com/questions/191757/c-concatenate-string-and-int#192242">linked it before</a> on SO.

blocks|key|1850985|text|You+may+want+to+read+my+prior+posting+on+SO.++(Macro'ed+version+with+a+temporary+ostringstream+object.)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1850986|郑重声明:在我自己的代码中，我更喜欢snprintf()。使用本地堆栈上的char数组，效率并不是很低。(好吧，如果超过数组大小并循环两次……)|1850987|(我还通过vsnprintf()对其进行了包装。但这会耗费我一些类型检查。Yelp，如果你想要代码...)|1850988|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/303562/c-format-macro-inline-ostringstream#306053^0|0|2V|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]]]]

<a href="https://stackoverflow.com/questions/303562/c-format-macro-inline-ostringstream#306053">You may want to read my prior posting on SO. (Macro'ed version with a temporary ostringstream object.)</a>

For the record: In my own code, I favor snprintf(). With a char array on the local stack, it's not that inefficient. (Well, maybe if you exceeded the array size and looped to do it twice...)

(I've also wrapped it via vsnprintf(). But that costs me some type checking. Yelp if you want the code...)

blocks|key|1851375|text|lexical_cast的问题在于无法定义精度。通常，如果您要将双精度值转换为字符串，这是因为您希望将其打印出来。如果精度太高或太低，都会影响输出。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1851376|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The problem with lexical_cast is the inability to define precision. Normally if you are converting a double to a string, it is because you want to print it out. If the precision is too much or too little, it would affect your output.

blocks|key|2065518|text|标准C%2B%2B11方式(如果您不关心输出格式)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2065519|#include+<string>

auto+str+=+std::to_string(42.5);+|code-block|syntax|javascript|2065520|to_string是N1803+(r0)、N1982+(r1)和N2408+(r2)“简单数值访问”中引入的新库函数。还可以使用stod函数执行相反的操作。|offset|length|style|CODE|2065521|如果您确实希望使用不同于"%25f"的输出格式，请使用snprintf或ostringstream方法，如其他答案中所示。|2065522|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/string/basic_string/to_string|1|http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1803.html|2|http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1982.html|3|http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2408.html^0|0|0|0|9|1S|4|0|9|0|A|5|1|L|5|2|W|5|3|0|C|4|P|8|Y|D|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@$I|15|J|16|K|L]|$I|17|J|18|K|L]]|9|@$I|19|J|1A|1|1B]|$I|1C|J|1D|1|1E]|$I|1F|J|1G|1|1H]|$I|1I|J|1J|1|1K]]|A|$]]|$1|M|3|N|5|6|7|1L|8|@$I|1M|J|1N|K|L]|$I|1O|J|1P|K|L]|$I|1Q|J|1R|K|L]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]|W|$5|R|S|T|A|$U|X]]|Y|$5|R|S|T|A|$U|Z]]|10|$5|R|S|T|A|$U|11]]]]

The Standard C++11 way (if you don't care about the output format):

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

auto str = std::to_string(42.5); 
</code></pre>

<a href="http://en.cppreference.com/w/cpp/string/basic_string/to_string" rel="noreferrer"><code>to_string</code></a> is a new library function introduced in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1803.html" rel="noreferrer">N1803</a> (r0), <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1982.html" rel="noreferrer">N1982</a> (r1) and <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2408.html" rel="noreferrer">N2408</a> (r2) "Simple Numeric Access". There are also the <code>stod</code> function to perform the reverse operation. 

If you do want to have a different output format than <code>"%f"</code>, use the <code>snprintf</code> or <code>ostringstream</code> methods as illustrated in other answers.

blocks|key|2065558|text|你可以尝试一种更紧凑的风格：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2065559|std::string+number_in_string;

double+number_in_double;

std::ostringstream+output;

number_in_string+=+(dynamic_cast<+std::ostringstream*>(&(output+<<+number_in_double+<<

std::endl)))->str();+|code-block|syntax|javascript|2065560|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 could try a more compact style:

<pre><code>std::string number_in_string;

double number_in_double;

std::ostringstream output;

number_in_string = (dynamic_cast&lt; std::ostringstream*&gt;(&amp;(output &lt;&lt; number_in_double &lt;&lt;

std::endl)))-&gt;str(); 
</code></pre>

blocks|key|1851485|text|我会看看C%2B%2B+String+Toolkit+Libary。只是在其他地方发布了类似的答案。我发现它非常快速和可靠。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1851486|#include+<strtk.hpp>

double+pi+=+M_PI;
std::string+pi_as_string++=+strtk::type_to_string<double>(+pi+);|code-block|syntax|javascript|1851487|entityMap|0|LINK|mutability|MUTABLE|url|http://www.partow.net/programming/strtk/index.html^0|4|P|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]]]]

I would look at the <a href="http://www.partow.net/programming/strtk/index.html" rel="nofollow noreferrer">C++ String Toolkit Libary</a>. Just posted a similar answer elsewhere. I have found it very fast and reliable.

<pre><code>#include &lt;strtk.hpp&gt;

double pi = M_PI;
std::string pi_as_string = strtk::type_to_string&lt;double&gt;( pi );
</code></pre>

blocks|key|2065628|text|通常，对于此操作，您必须使用ecvt、fcvt或gcvt函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2065629|/*+gcvt+example+*/
#include+<stdio.h>
#include+<stdlib.h>

main+()
{
++char+buffer+[20];
++gcvt+(1365.249,6,buffer);
++puts+(buffer);
++gcvt+(1365.249,3,buffer);
++puts+(buffer);
++return+0;
}

Output:
1365.25
1.37e%2B003+++|code-block|syntax|javascript|2065630|作为函数：|2065631|void+double_to_char(double+f,char+*+buffer){
++gcvt(f,10,buffer);
}|2065632|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|$]]

Normaly for this operations you have to use the ecvt, fcvt or gcvt Functions:

<pre><code>/* gcvt example */
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;

main ()
{
 char buffer [20];
 gcvt (1365.249,6,buffer);
 puts (buffer);
 gcvt (1365.249,3,buffer);
 puts (buffer);
 return 0;
}

Output:
1365.25
1.37e+003 
</code></pre>

As a Function:

<pre><code>void double_to_char(double f,char * buffer){
 gcvt(f,10,buffer);
}
</code></pre>

blocks|key|1851558|text|使用to_string()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1851559|示例：|1851560|#include+<iostream>+++
#include+<string>++

using+namespace+std;
int+main+()
{
++++string+pi+=+"pi+is+"+%2B+to_string(3.1415926);
++++cout<<+"pi+=+"<<+pi+<<+endl;

++return+0;
}|code-block|syntax|javascript|1851561|自己运行：http://ideone.com/7ejfaU|1851562|这些也是可用的：|1851563|string+to_string+(int+val);
string+to_string+(long+val);
string+to_string+(long+long+val);
string+to_string+(unsigned+val);
string+to_string+(unsigned+long+val);
string+to_string+(unsigned+long+long+val);
string+to_string+(float+val);
string+to_string+(double+val);
string+to_string+(long+double+val);|1851564|entityMap|0|LINK|mutability|MUTABLE|url|http://ideone.com/7ejfaU^0|2|B|0|0|0|5|O|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@]|D|@$9|16|A|17|1|18]]|E|$]]|$1|O|3|P|5|6|7|19|8|@]|D|@]|E|$]]|$1|Q|3|R|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|S|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

Use <code>to_string()</code>. 
example : 

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

using namespace std;
int main ()
{
 string pi = "pi is " + to_string(3.1415926);
 cout&lt;&lt; "pi = "&lt;&lt; pi &lt;&lt; endl;

 return 0;
}
</code></pre>

run it yourself : <a href="http://ideone.com/7ejfaU" rel="nofollow">http://ideone.com/7ejfaU</a> 
These are available as well : 

<pre><code>string to_string (int val);
string to_string (long val);
string to_string (long long val);
string to_string (unsigned val);
string to_string (unsigned long val);
string to_string (unsigned long long val);
string to_string (float val);
string to_string (double val);
string to_string (long double val);
</code></pre>

blocks|key|1851612|text|您可以使用此函数将任何内容转换为任何内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1851613|template<class+T+=+std::string,+class+U>
T+to(U+a)+{
++++std::stringstream+ss;
++++T+ret;
++++ss+<<+a;
++++ss+>>+ret;
++++return+ret;
};|code-block|syntax|javascript|1851614|用法：|1851615|std::string+str+=+to(2.5);
double+d+=+to<double>("2.5");|1851616|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|$]]

You can convert any thing to anything using this function:

<pre><code>template&lt;class T = std::string, class U&gt;
T to(U a) {
 std::stringstream ss;
 T ret;
 ss &lt;&lt; a;
 ss &gt;&gt; ret;
 return ret;
};
</code></pre>

usage :

<pre><code>std::string str = to(2.5);
double d = to&lt;double&gt;("2.5");
</code></pre>

blocks|key|2065802|text|请注意，字符串只是双精度值的表示形式，将其转换回双精度值可能不会产生相同的值。另请注意，默认字符串转换可能会将转换修整到一定的精度。在标准的C%2B%2B方式中，您可以按如下方式控制精度：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2065803|#include+<sstream>
#include+<math.h>
#include+<iostream>
#include+<iomanip>

int+main()
{
++++std::ostringstream+sout;
++++sout+<<+M_PI+<<+'\n';
++++sout+<<+std::setprecision(99)+<<+M_PI+<<+'\n';
++++sout+<<+std::setprecision(3)+<<+M_PI+<<+'\n';
++++sout+<<+std::fixed;+//now+the+setprecision()+value+will+look+at+the+decimal+part+only.
++++sout+<<+std::setprecision(3)+<<+M_PI+<<+'\n';
++++std::cout+<<+sout.str();
}|code-block|syntax|javascript|2065804|这将为您提供输出|2065805|3.14159++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
3.141592653589793115997963468544185161590576171875+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
3.14+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
3.142++|2065806|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|$]]

Note that a string is just a representation of the double and converting it back to double may not result in the same value.
Also note that the default string conversion may trim the conversion to a certain precision.
In the standard C++ way, you can control the precision as follows:
<pre><code>#include &lt;sstream&gt;
#include &lt;math.h&gt;
#include &lt;iostream&gt;
#include &lt;iomanip&gt;

int main()
{
 std::ostringstream sout;
 sout &lt;&lt; M_PI &lt;&lt; '\n';
 sout &lt;&lt; std::setprecision(99) &lt;&lt; M_PI &lt;&lt; '\n';
 sout &lt;&lt; std::setprecision(3) &lt;&lt; M_PI &lt;&lt; '\n';
 sout &lt;&lt; std::fixed; //now the setprecision() value will look at the decimal part only.
 sout &lt;&lt; std::setprecision(3) &lt;&lt; M_PI &lt;&lt; '\n';
 std::cout &lt;&lt; sout.str();
}
</code></pre>
which will give you the output
<pre><code>3.14159 
3.141592653589793115997963468544185161590576171875 
3.14 
3.142 
</code></pre>

I need to store a double as a string. I know I can use <code>printf</code> if I wanted to display it, but I just want to store it in a string variable so that I can store it in a map later (as the value, not the key).

How do I convert a double into a string in C++?

我需要将双精度值存储为字符串。我知道如果我想要显示它，我可以使用printf，但我只想将它存储在一个字符串变量中，以便以后可以将它存储在一个映射中(作为值，而不是键)。

问如何在C++中将双精度值转换为字符串？
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