blocks|key|1432860|text|好吧，只使用字符，而不是整数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1432861|s+<<+char(1)+<<+char(2)+<<+char(3);|code-block|syntax|javascript|1432862|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|$]]

Well, just use characters, not integers.

<pre><code>s &lt;&lt; char(1) &lt;&lt; char(2) &lt;&lt; char(3);
</code></pre>

blocks|key|1432986|text|要向流(包括字符串流)读写二进制数据，请使用read()和write()成员函数。所以|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1432987|unsigned+char+a(1),+b(2),+c(3),+d(4);
std::stringstream+s;
s.write(reinterpret_cast<const+char*>(&a),+sizeof(unsigned+char));
s.write(reinterpret_cast<const+char*>(&b),+sizeof(unsigned+char));
s.write(reinterpret_cast<const+char*>(&c),+sizeof(unsigned+char));
s.write(reinterpret_cast<const+char*>(&d),+sizeof(unsigned+char));

s.read(reinterpret_cast<char*>(&v),+sizeof(unsigned+int));+
std::cout+<<+std::hex+<<+v+<<+"\n";|code-block|syntax|javascript|1432988|这在我的系统上提供了0x4030201。|offset|length|style|CODE|1432989|编辑:为了使用插入和提取操作符(<<和>>)透明地工作，您最好创建一个派生的streambuf来做正确的事情，并将其传递给您想要使用的任何流。|1432990|entityMap^0|0|0|A|9|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

To read and write binary data to streams, including stringstreams, use the read() and write() member functions. So

<pre><code>unsigned char a(1), b(2), c(3), d(4);
std::stringstream s;
s.write(reinterpret_cast&lt;const char*&gt;(&amp;a), sizeof(unsigned char));
s.write(reinterpret_cast&lt;const char*&gt;(&amp;b), sizeof(unsigned char));
s.write(reinterpret_cast&lt;const char*&gt;(&amp;c), sizeof(unsigned char));
s.write(reinterpret_cast&lt;const char*&gt;(&amp;d), sizeof(unsigned char));

s.read(reinterpret_cast&lt;char*&gt;(&amp;v), sizeof(unsigned int)); 
std::cout &lt;&lt; std::hex &lt;&lt; v &lt;&lt; "\n";
</code></pre>

This gives <code>0x4030201</code> on my system. 

Edit:
To make this work transparently with the insertion and extraction operators (&lt;&lt; and >>), your best bet it to create a derived streambuf that does the right thing, and pass that to whatever streams you want to use.

blocks|key|1433045|text|你可以用模板来做这类事情。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1433046|//struct+to+hold+the+value:
template<typename+T>+struct+bits_t+{+T+t;+};+//no+constructor+necessary
//functions+to+infer+type,+construct+bits_t+with+a+member+initialization+list
//use+a+reference+to+avoid+copying.+The+non-const+version+lets+us+extract+too
template<typename+T>+bits_t<T&>+bits(T+&t)+{+return+bits_t<T&>{t};+}
template<typename+T>+bits_t<const+T&>+bits(const+T&+t)+{+return+bits_t<const+T&>{t};+}
//insertion+operator+to+call+::write()+on+whatever+type+of+stream
template<typename+S,+typename+T>
S&+operator<<(S+&s,+bits_t<T>+b)+{
++++return+s.write((char*)&b.t,+sizeof(T));
}
//extraction+operator+to+call+::read(),+require+a+non-const+reference+here
template<typename+S,+typename+T>
S&+operator>>(S&+s,+bits_t<T&>+b)+{
++++return+s.read((char*)&b.t,+sizeof(T));
}|code-block|syntax|javascript|1433047|它可能需要一些清理，但它是有功能的。例如：|1433048|//writing
std::ofstream+f+=+/*open+a+file*/;
int+a+=+5,+b+=+-1,+c+=+123456;
f+<<+bits(a)+<<+bits(b)+<<+bits(c);

//reading
std::ifstream+f2+=+/*open+a+file*/;
int+a,+b,+c;
f+>>+bits(a)+>>+bits(b)+>>+bits(c);|1433049|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 do this sort of thing with templates. E.g:

<pre><code>//struct to hold the value:
template&lt;typename T&gt; struct bits_t { T t; }; //no constructor necessary
//functions to infer type, construct bits_t with a member initialization list
//use a reference to avoid copying. The non-const version lets us extract too
template&lt;typename T&gt; bits_t&lt;T&amp;&gt; bits(T &amp;t) { return bits_t&lt;T&amp;&gt;{t}; }
template&lt;typename T&gt; bits_t&lt;const T&amp;&gt; bits(const T&amp; t) { return bits_t&lt;const T&amp;&gt;{t}; }
//insertion operator to call ::write() on whatever type of stream
template&lt;typename S, typename T&gt;
S&amp; operator&lt;&lt;(S &amp;s, bits_t&lt;T&gt; b) {
 return s.write((char*)&amp;b.t, sizeof(T));
}
//extraction operator to call ::read(), require a non-const reference here
template&lt;typename S, typename T&gt;
S&amp; operator&gt;&gt;(S&amp; s, bits_t&lt;T&amp;&gt; b) {
 return s.read((char*)&amp;b.t, sizeof(T));
}
</code></pre>

It could use some cleanup, but it's functional. E.g:

<pre><code>//writing
std::ofstream f = /*open a file*/;
int a = 5, b = -1, c = 123456;
f &lt;&lt; bits(a) &lt;&lt; bits(b) &lt;&lt; bits(c);

//reading
std::ifstream f2 = /*open a file*/;
int a, b, c;
f &gt;&gt; bits(a) &gt;&gt; bits(b) &gt;&gt; bits(c);
</code></pre>

blocks|key|1218280|text|#include+<sstream>

class+bostringstream+{
public:
++bostringstream()+:+oss()+{}

++template+<typename+T,+typename+std::enable_if<std::is_fundamental<T>::value,
++++++++++++++++++++++++++++++++++++++++++++++++bool>::type+=+true>
++bostringstream&+operator<<(const+T&+v)+{
++++oss.write((char*)&v,+sizeof(T));
++++return+*this;
++}

++template+<typename+T,+typename+std::enable_if<
++++++++++++++++++++++++++++std::is_fundamental<typename+T::value_type>::value,
++++++++++++++++++++++++++++bool>::type+=+true>
++bostringstream&+operator<<(const+T&+v)+{
++++oss.write((char*)v.data(),+v.size()+*+sizeof(typename+T::value_type));
++++return+*this;
++}

++template+<typename+_InputIterator>
++bostringstream&+write(_InputIterator+first,+_InputIterator+last)+{
++++char*+data+=+(char*)&(*first);
++++auto+n+=+std::distance(first,+last);
++++oss.write(data,+n+*+sizeof(*first));
++++return+*this;
++}

++template+<typename+T,+typename+std::enable_if<std::is_fundamental<T>::value,
++++++++++++++++++++++++++++++++++++++++++++++++bool>::type+=+true>
++bostringstream&+write(const+T*+v,+std::streamsize+count)+{
++++oss.write((char*)v,+sizeof(T)+*+count);
++++return+*this;
++}

++auto+rdbuf()+const+{+return+oss.rdbuf();+}

++auto+str()+const+{+return+oss.str();+}

++std::size_t+size()+{+return+oss.tellp();+}

protected:
++std::ostringstream+oss;
};|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1218281|示例：|unstyled|1218282|#include+<array>
#include+<string>
#include+<vector>
#include+<iostream>
#include+<fstream>
#include+"bsstream.hpp"

int+main(int+argc,+char+**argv)+{

++int+i+=+1;
++float+j+=+1.1;
++double+k+=+1.2;
++std::vector<int>+ii{1,2};
++std::vector<double>+jj{1.2,2.2};
++std::string+kk+=+"abcd";
++std::array<int,+2>+ll{3,4};
++int+l[]+=+{1,2};

++bostringstream+of;
++of+<<+i+<<+j+<<k;
++of+<<ii+<<+jj+<<+kk+<<+ll;
++of.write(l,+2);

++std::ofstream+oof("foo.bin",+std::ios::binary);
++oof+<<+of.str();
++oof.close();

}|1218283|不是一个优雅的解决方案，但工作灵活|1218284|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<pre class="lang-cpp prettyprint-override"><code>#include &lt;sstream&gt;

class bostringstream {
public:
 bostringstream() : oss() {}

 template &lt;typename T, typename std::enable_if&lt;std::is_fundamental&lt;T&gt;::value,
 bool&gt;::type = true&gt;
 bostringstream&amp; operator&lt;&lt;(const T&amp; v) {
 oss.write((char*)&amp;v, sizeof(T));
 return *this;
 }

 template &lt;typename T, typename std::enable_if&lt;
 std::is_fundamental&lt;typename T::value_type&gt;::value,
 bool&gt;::type = true&gt;
 bostringstream&amp; operator&lt;&lt;(const T&amp; v) {
 oss.write((char*)v.data(), v.size() * sizeof(typename T::value_type));
 return *this;
 }

 template &lt;typename _InputIterator&gt;
 bostringstream&amp; write(_InputIterator first, _InputIterator last) {
 char* data = (char*)&amp;(*first);
 auto n = std::distance(first, last);
 oss.write(data, n * sizeof(*first));
 return *this;
 }

 template &lt;typename T, typename std::enable_if&lt;std::is_fundamental&lt;T&gt;::value,
 bool&gt;::type = true&gt;
 bostringstream&amp; write(const T* v, std::streamsize count) {
 oss.write((char*)v, sizeof(T) * count);
 return *this;
 }

 auto rdbuf() const { return oss.rdbuf(); }

 auto str() const { return oss.str(); }

 std::size_t size() { return oss.tellp(); }

protected:
 std::ostringstream oss;
};
</code></pre>
Example:
<pre><code>#include &lt;array&gt;
#include &lt;string&gt;
#include &lt;vector&gt;
#include &lt;iostream&gt;
#include &lt;fstream&gt;
#include &quot;bsstream.hpp&quot;

int main(int argc, char **argv) {

 int i = 1;
 float j = 1.1;
 double k = 1.2;
 std::vector&lt;int&gt; ii{1,2};
 std::vector&lt;double&gt; jj{1.2,2.2};
 std::string kk = &quot;abcd&quot;;
 std::array&lt;int, 2&gt; ll{3,4};
 int l[] = {1,2};

 bostringstream of;
 of &lt;&lt; i &lt;&lt; j &lt;&lt;k;
 of &lt;&lt;ii &lt;&lt; jj &lt;&lt; kk &lt;&lt; ll;
 of.write(l, 2);

 std::ofstream oof(&quot;foo.bin&quot;, std::ios::binary);
 oof &lt;&lt; of.str();
 oof.close();

}
</code></pre>
Not an elegant solution but works and flexible

I usually use <code>stringstream</code> to write into in-memory string. Is there a way to write to a char buffer in binary mode? Consider the following code:

<pre><code>stringstream s;
s &lt;&lt; 1 &lt;&lt; 2 &lt;&lt; 3;
const char* ch = s.str().c_str();
</code></pre>

The memory at <code>ch</code> will look like this: 0x313233 - the ASCII codes of the characters 1, 2 and 3. I'm looking for a way to write the binary values themselves. That is, I want 0x010203 in the memory. The problem is that I want to be able to write a function

<pre><code>void f(ostream&amp; os)
{
 os &lt;&lt; 1 &lt;&lt; 2 &lt;&lt; 3;
}
</code></pre>

And decide outside what kind of stream to use. Something like this:

<pre><code>mycharstream c;
c &lt;&lt; 1 &lt;&lt; 2 &lt;&lt; 3; // c.data == 0x313233;
mybinstream b;
b &lt;&lt; 1 &lt;&lt; 2 &lt;&lt; 3; // b.data == 0x010203;
</code></pre>

Any ideas?

Are there binary memory streams in C++

我通常使用stringstream来写入内存中的字符串。有没有办法在二进制模式下写入字符缓冲区？考虑以下代码：stringstream s;s << 1 << 2 << 3;const char* ch = s.str().c_str();ch的内存将如下所示: 0x313233 -字符1、2和3的ASCII码。我正在...

问C++中是否存在二进制内存流
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