blocks|key|91364|text|您正在将double的文字字节转换为chars。double值是二进制表示(通常类似于IEEE+754)，而char是字符的二进制表示(通常基于ASCII)。这两个不兼容。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|91365|不幸的是，这意味着您必须进行某种转换过程。要么是你说你不想做的std::to_string()，要么是一个更复杂的std::stringbuf+(它无论如何都会在幕后调用std::to_string()+)|91366|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/Double-precision_floating-point_format|1|https://en.wikipedia.org/wiki/ASCII^0|4|6|I|4|O|6|1I|4|17|8|0|20|5|1|0|V|G|1L|E|2D|G|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@$9|10|A|11|1|12]|$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]]]

You are translating the literal bytes of your <code>double</code> into <code>char</code>s. The <code>double</code> value is a binary representation (usually something like <a href="https://en.wikipedia.org/wiki/Double-precision_floating-point_format" rel="noreferrer">IEEE 754</a>) while a <code>char</code> is a binary representation of a character (usually something based on <a href="https://en.wikipedia.org/wiki/ASCII" rel="noreferrer">ASCII</a>). These two are not compatible.

Unfortunately, this means that you must do some kind of conversion process. Either the <code>std::to_string()</code> that you said you don't want to do, or a more complicated <code>std::stringbuf</code> (which will call <code>std::to_string()</code> under the hood anyway)

blocks|key|91311|text|您正在将一个double+(数字的二进制表示形式)复制到char数组中；这些字节没有理由与数字字符相对应。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|91312|entityMap^0|6|6|S|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

You are copying a <code>double</code> (which is a binary representation for a number) into a <code>char</code> array; there is no reason those bytes should correspond to digit characters.

blocks|key|2829753|text|这并未经过测试，但您可以尝试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2829754|std::string+to_string(double+x)
{
++++std::ostringstream+ss;
++++ss+<<+x;
++++return+ss.str();
}|code-block|syntax|javascript|2829755|然后，您可以将返回字符串的字符放入char数组中，如下所示：|2829756|std::string+str+=+to_string(doubleValue);
char+digits[str.length()];|2829757|然后，多亏了Remy+Lebeau的评论，你可以这样做：|2829758|std::strncpy(digits,+to_string(doubleValue).c_str(),+sizeof(digits))|2829759|或者这样：|2829760|to_string(doubleValue).copy(digits,+sizeof(digits))|2829761|entityMap^0|0|0|0|0|0|0|0|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]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

This isn’t tested but you could try:

<pre><code>std::string to_string(double x)
{
 std::ostringstream ss;
 ss &lt;&lt; x;
 return ss.str();
}
</code></pre>

You could then put the returned string’s characters into a char array like this:

<pre><code>std::string str = to_string(doubleValue);
char digits[str.length()];
</code></pre>

And then, thanks to the comment from Remy Lebeau, you can do either this:

<pre><code>std::strncpy(digits, to_string(doubleValue).c_str(), sizeof(digits))
</code></pre>

or this:

<pre><code>to_string(doubleValue).copy(digits, sizeof(digits))
</code></pre>

blocks|key|2617952|text|如果你想在不使用to_string的情况下手动转换，你必须一次取出一个数字。double不是作为一组字符存储在内存中的，所以您不能只是复制内存并希望它都能正常工作。(有关如何解释doubles的更多信息，请参见here)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2617953|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/IEEE_754^0|8|9|2X|4|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

If you want to convert by hand without using <code>to_string</code>, you're going to have to pull digits out one at a time. A double isn't stored in memory as a set of characters, so you can't just copy over the memory and hope it all works. (for more on how doubles are interpreted, see <a href="https://en.wikipedia.org/wiki/IEEE_754" rel="nofollow noreferrer">here</a>).

blocks|key|93763|text|只需先使用do+this：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|93764|std::ostringstream+strs;
strs+<<+dbl;
std::string+str+=+strs.str();|code-block|syntax|javascript|93765|这会将双精度dbl转换为字符串str。|style|CODE|93766|然后，您可以将其转换为一个字符数组，如下所示：|93767|char+*cstr+=+new+char[str.length()%2B1];
str.copy(cstr,+str.length());
cstr[str.length()]+=+'\0';
//+use+cstr+as+needed...
delete[]+cstr;|93768|或者，简单地说：|93769|const+char+*cstr+=+str.c_str();
//+use+cstr+as+needed...|93770|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/332132/3294286^0|5|7|0|0|0|6|3|F|3|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|17|8|@$A|18|B|19|K|L]|$A|1A|B|1B|K|L]]|9|@]|C|$]]|$1|M|3|N|5|6|7|1C|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1D|8|@]|9|@]|C|$G|H]]|$1|Q|3|R|5|6|7|1E|8|@]|9|@]|C|$]]|$1|S|3|T|5|F|7|1F|8|@]|9|@]|C|$G|H]]|$1|U|3|-4|5|6|7|1G|8|@]|9|@]|C|$]]]|V|$W|$5|X|Y|Z|C|$10|11]]]]

Just <a href="https://stackoverflow.com/a/332132/3294286">do this</a> first:

<pre><code>std::ostringstream strs;
strs &lt;&lt; dbl;
std::string str = strs.str();
</code></pre>

This converts a double <code>dbl</code> to a string <code>str</code>.

Then you can convert it to an array of chars like this:

<pre><code>char *cstr = new char[str.length()+1];
str.copy(cstr, str.length());
cstr[str.length()] = '\0';
// use cstr as needed...
delete[] cstr;
</code></pre>

Or, simply this:

<pre><code>const char *cstr = str.c_str();
// use cstr as needed...
</code></pre>

blocks|key|93772|text|在不使用to_string的情况下自行转换的过程可能如下：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|93773|char*+to_char_array(double+num_double,+int+decimal_place)
{
++++int+num_int+=+std::round(num_double+*+pow(10,+decimal_place));
++++int+sign+=+num_int+<+0+?+1+:+0;
++++num_int+=+abs(num_int);

++++if+(num_int+==+0)
++++{
++++++++char*+s+=+(char*)malloc(decimal_place+%2B+3);
++++++++s[0]+=+'0';
++++++++s[1]+=+'.';
++++++++for+(int+i+=+2;+i+<+decimal_place+%2B+2;+i%2B%2B)
++++++++++++s[i]+=+'0';
++++++++s[decimal_place+%2B+2]+=+'\0';
++++++++return+s;
++++}

++++int+digit_count+=+1;
++++int+n+=+num_int;
++++if+(n+>=+100000000)+{+digit_count+%2B=+8;+n+/=+100000000;+}
++++if+(n+>=+10000)+{+digit_count+%2B=+4;+n+/=+10000;+}
++++if+(n+>=+100)+{+digit_count+%2B=+2;+n+/=+100;+}
++++if+(n+>=+10)+{+digit_count%2B%2B;+}

++++int+size+=+digit_count+%2B+1+%2B+(decimal_place+>+0+?+1+:+0)+%2B+sign;
++++char*+s+=+(char*)malloc(size);

++++for+(int+i+=+0,+integer+=+num_int;+integer+!=+0;+integer+/=+10)+{
++++++++s[size+-+2+-+i%2B%2B]+=+integer+%25+10+%2B+48;
++++++++if+(decimal_place+>+0+&&+i+==+decimal_place)
++++++++++++s[size+-+2+-+i%2B%2B]+=+'.';
++++}
++++s[size+-+1]+=+'\0';
++++if+(sign)
++++++++s[0]+=+'-';
++++return+s;
}

void+main()
{
++++double+d+=+-12.268904;
++++char*+s+=+to_char_array(d,+3);
++++cout+<<+"double:+"+<<+d+<<+"+-+char+array:+"+<<+s+<<+endl;
++++system("pause");
}|code-block|syntax|javascript|93774|entityMap^0|4|9|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

The conversion process by your self without using <code>to_string</code> may be as follow:

<pre><code>char* to_char_array(double num_double, int decimal_place)
{
 int num_int = std::round(num_double * pow(10, decimal_place));
 int sign = num_int &lt; 0 ? 1 : 0;
 num_int = abs(num_int);

 if (num_int == 0)
 {
 char* s = (char*)malloc(decimal_place + 3);
 s[0] = '0';
 s[1] = '.';
 for (int i = 2; i &lt; decimal_place + 2; i++)
 s[i] = '0';
 s[decimal_place + 2] = '\0';
 return s;
 }

 int digit_count = 1;
 int n = num_int;
 if (n &gt;= 100000000) { digit_count += 8; n /= 100000000; }
 if (n &gt;= 10000) { digit_count += 4; n /= 10000; }
 if (n &gt;= 100) { digit_count += 2; n /= 100; }
 if (n &gt;= 10) { digit_count++; }

 int size = digit_count + 1 + (decimal_place &gt; 0 ? 1 : 0) + sign;
 char* s = (char*)malloc(size);

 for (int i = 0, integer = num_int; integer != 0; integer /= 10) {
 s[size - 2 - i++] = integer % 10 + 48;
 if (decimal_place &gt; 0 &amp;&amp; i == decimal_place)
 s[size - 2 - i++] = '.';
 }
 s[size - 1] = '\0';
 if (sign)
 s[0] = '-';
 return s;
}

void main()
{
 double d = -12.268904;
 char* s = to_char_array(d, 3);
 cout &lt;&lt; "double: " &lt;&lt; d &lt;&lt; " - char array: " &lt;&lt; s &lt;&lt; endl;
 system("pause");
}
</code></pre>

blocks|key|94173|text|只需执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|94174|++#include+<iostream>
++#include+<string>
++#include+<sstream>

++using+namespace+std;

++int+main()
++{
++++++double+a=23.25;
++++++char+b[12];
++++++stringstream+ss;

++++++ss+<<+a;
++++++ss+>>+b;
++++++cout+<<+b+<<+endl;

++++++return+0;
++}|code-block|syntax|javascript|94175|或者这样：|94176|++#include+<iostream>
++#include+<string>
++#include+<sstream>
++#include+<stdio.h>


++using+namespace+std;

++int+main()
++{


++double+a=23.25;
++char+b[12];
++stringstream+ss++;
++ss<<a;
++sprintf(b,ss.str().c_str());
++cout<<b<<endl;
++return+0;|94177|94178|​|94179|here+don't+forget+to
+#include<bits/stdc%2B%2B.h>
++
++double+a=23.25;
++char+b[12];
++stringstream+ss++;
++ss<<a;
++strcpy(b,ss.str().c_str());
++cout<<b<<endl;
++return+0;|94180|94181|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|X|8|@]|9|@]|A|$]]|$1|N|3|O|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|P|3|M|5|6|7|Z|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|R|$]]

just do this:

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

 using namespace std;

 int main()
 {
 double a=23.25;
 char b[12];
 stringstream ss;

 ss &lt;&lt; a;
 ss &gt;&gt; b;
 cout &lt;&lt; b &lt;&lt; endl;

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

or this:

<pre><code> #include &lt;iostream&gt;
 #include &lt;string&gt;
 #include &lt;sstream&gt;
 #include &lt;stdio.h&gt;


 using namespace std;

 int main()
 {


 double a=23.25;
 char b[12];
 stringstream ss ;
 ss&lt;&lt;a;
 sprintf(b,ss.str().c_str());
 cout&lt;&lt;b&lt;&lt;endl;
 return 0;
</code></pre>

or this:

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-css lang-css prettyprint-override"><code>here don't forget to
 #include&lt;bits/stdc++.h&gt;
 
 double a=23.25;
 char b[12];
 stringstream ss ;
 ss&lt;&lt;a;
 strcpy(b,ss.str().c_str());
 cout&lt;&lt;b&lt;&lt;endl;
 return 0;</code></pre>
</div>
</div>

I'm trying to convert (and round) a double to a char array without converting with a std::to_string on the double first. However, I'm receiving random memory text instead. What am I doing wrong? 

Here is my code:

<pre><code>double d = 1.0929998; 
d = std::round(d * 100) / 100;

char s[sizeof(d)];
std::memcpy(s,&amp;d,sizeof(d));
</code></pre>

Result:

<blockquote>
 s: q=×£pñ?
</blockquote>

Intended value: 

<blockquote>
 s: 1.09
</blockquote>

Convert double to Char Array C++

我尝试转换(并舍入)一个双精度数组为字符数组，而不是先在双精度数组上使用std::to_string进行转换。然而，我收到的却是随机的内存文本。我做错了什么？下面是我的代码：double d = 1.0929998; d = std::round(d * 100) / 100;char s[sizeof(d)];std::memcpy(s,&d,sizeof(d));结果： s: q=×£pñ？目

问将double转换为字符数组C++
EN

回答 7

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问将double转换为字符数组C++
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