blocks|key|4581161|text|如果函数foo没有复制字符串，那么它接口就不是最优的。最好将其更改为接受char+const*或string_view，这样调用者就不需要构造std::string。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4581162|或者添加重载：|4581163|void+foo(char+const*+str,+size_t+str_len);+//+Does+real+work.

inline+void+foo(std::string+const&+s)+{+foo(s.data(),+s.size());+}
inline+void+foo(char+const*+s)+{+foo(s,+strlen(s));+}|code-block|syntax|javascript|4581164|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/header/experimental/string_view^0|4|3|10|B|1C|B|1Z|B|1C|B|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|17|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

If that function <code>foo</code> does not make a copy of the string then its interface is sub-optimal. It is better to change it to accept <code>char const*</code> or <a href="http://en.cppreference.com/w/cpp/header/experimental/string_view"><code>string_view</code></a>, so that the caller is not required to construct <code>std::string</code>. 

Or add overloads:

<pre><code>void foo(char const* str, size_t str_len); // Does real work.

inline void foo(std::string const&amp; s) { foo(s.data(), s.size()); }
inline void foo(char const* s) { foo(s, strlen(s)); }
</code></pre>

blocks|key|4581244|text|您可以使用Boost.Flyweight创建从const+char*到std::string的key-value+flyweight。我不确定细节，可能是到处使用flyweight<std::string>就足够了。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4581245|entityMap|0|LINK|mutability|MUTABLE|url|http://www.boost.org/doc/libs/1_56_0/libs/flyweight/doc/index.html|1|http://www.boost.org/doc/libs/1_56_0/libs/flyweight/doc/tutorial/key_value.html^0|N|B|Z|B|29|M|5|F|0|1B|J|1|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|@$9|W|A|X|1|Y]|$9|Z|A|10|1|11]]|E|$]]|$1|F|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]|N|$5|I|J|K|E|$L|O]]]]

You could use <a href="http://www.boost.org/doc/libs/1_56_0/libs/flyweight/doc/index.html" rel="nofollow">Boost.Flyweight</a> to make a <a href="http://www.boost.org/doc/libs/1_56_0/libs/flyweight/doc/tutorial/key_value.html" rel="nofollow">key-value flyweight</a> from <code>const char*</code> to <code>std::string</code>. I'm not sure about the details, might be that it is enough to use <code>flyweight&lt;std::string&gt;</code> everywhere.

blocks|key|4581271|text|这将适用于简单的字符串-没有空格：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4581272|#define+DECL_STR(s)+const+std::string+str_##s+(#s)|code-block|syntax|javascript|4581273|头部用法(解析一次！)：|4581274|DECL_STR(Foo);
DECL_STR(Bar);|4581275|在代码中：|4581276|func(str_Foo);
func(str_Bar);|4581277|entityMap^0|0|0|0|0|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]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

This will work for simple strings - w/o whitespace:

<pre><code>#define DECL_STR(s) const std::string str_##s (#s)
</code></pre>

Usage in header (parse once!):

<pre><code>DECL_STR(Foo);
DECL_STR(Bar);
</code></pre>

In code:

<pre><code>func(str_Foo);
func(str_Bar);
</code></pre>

blocks|key|4581296|text|如果您可以使用Boost1.55或更高版本，则可以|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4581297|#include+<boost/utility/string_ref.hpp>

void+foo(const+boost::string_ref&+xyz)
{
}|code-block|syntax|javascript|4581298|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 can use boost 1.55 or greater you can do

<pre><code>#include &lt;boost/utility/string_ref.hpp&gt;

void foo(const boost::string_ref&amp; xyz)
{
}
</code></pre>

Suppose I need to call a function <code>foo</code> that takes a const <code>std::string</code> reference from a great number of places in my code:

<pre><code>int foo(const std::string&amp;);
..
foo("bar");
..
foo("baz");
</code></pre>

Calling a function with a string literal like this will create temporary <code>std::string</code> objects, copying the literal each time.

Unless I'm mistaken, compilers won't optimize this by creating a static <code>std::string</code> object per literal that can be reused for subsequent calls. I know that g++ has advanced string pool mechanisms, but I don't think it extends to the <code>std::string</code> objects themselves.

I can do this "optimization" myself, which makes the code somewhat less readable:

<pre><code>static std::string bar_string("bar");
foo(bar_string);
..
static std::string baz_string("baz");
foo(baz_string);
</code></pre>

Using Callgrind, I can confirm that this does indeed speed up my program.

I thought I'd try to make a macro for this, but I don't know if it's possible. What I would want is something like:

<pre><code>foo(STATIC_STRING("bar"));
..
foo(STATIC_STRING("baz"));
</code></pre>

I tried creating a template with the literal as a template parameter, but that proved impossible. And since a function definition in a code block isn't possible, I'm all out of ideas.

Is there an elegant way of doing this, or will I have to resort to the less readable solution?

Macro for static std::string object from literal

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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假设我需要调用一个从代码中大量位置获取常量std::string引用的函数foo：int foo(const std::string&);..foo("bar");..foo("baz");像这样使用字符串文字调用函数将创建临时std::string对象，每次都会复制文字。除非我弄错了，否则编译器不会通过为每个文本创建...

问来自文本的静态std::string对象的宏
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