blocks|key|1262927|text|您可以使用C%2B%2B11使用constexpr函数来完成此操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1262928|constexpr+bool+strings_equal(char+const+*+a,+char+const+*+b)+{
++++return+*a+==+*b+&&+(*a+==+'\0'+%7C%7C+strings_equal(a+%2B+1,+b+%2B+1));
}|code-block|syntax|javascript|1262929|(见演示)|1262930|在C%2B%2B11之前是不可能这样做的，但是需要注意的是，许多编译器将编译相同的字符串文本作为指向同一位置的指针。在这些编译器上，直接比较字符串就足够了，因为它们都将被计算为相等的指针。|1262931|entityMap|0|LINK|mutability|MUTABLE|url|http://ideone.com/qf4Edn^0|C|9|0|0|1|3|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|D|@$9|11|A|12|1|13]]|E|$]]|$1|M|3|N|5|6|7|14|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

You can do this with C++11 by using a <code>constexpr</code> function:

<pre><code>constexpr bool strings_equal(char const * a, char const * b) {
 return *a == *b &amp;&amp; (*a == '\0' || strings_equal(a + 1, b + 1));
}
</code></pre>

(<a href="http://ideone.com/qf4Edn" rel="noreferrer">See a demo</a>)

It's not possible to do this prior to C++11, with the caveat that many compilers will compile equal string literals to be a pointer to the same location. On these compilers it's sufficient to compare the strings directly since they will both be evaluated as equal pointers.

blocks|key|1607447|text|从C%2B%2B17开始，视图是可用的。它支持比较箱：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1607448|#include+<string_view>

constexpr+bool+strings_equal(char+const+*+a,+char+const+*+b)+{
++++return+std::string_view(a)==b;
}

int+main()+{
++++static_assert(strings_equal("abc",+"abc"+),+"strings+are+equal");
++++static_assert(!strings_equal("abc",+"abcd"),+"strings+are+not+equal");
++++return+0;
}|code-block|syntax|javascript|1607449|演示|1607450|entityMap|0|LINK|mutability|MUTABLE|url|https://en.cppreference.com/w/cpp/string/basic_string_view|1|http://coliru.stacked-crooked.com/a/d85e5dd073589628^0|9|2|0|0|0|0|2|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

Starting with C++17 <a href="https://en.cppreference.com/w/cpp/string/basic_string_view" rel="noreferrer">std::string_view</a> is available. It supports constexpr comparisson:

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

constexpr bool strings_equal(char const * a, char const * b) {
 return std::string_view(a)==b;
}

int main() {
 static_assert(strings_equal("abc", "abc" ), "strings are equal");
 static_assert(!strings_equal("abc", "abcd"), "strings are not equal");
 return 0;
}
</code></pre>

<a href="http://coliru.stacked-crooked.com/a/d85e5dd073589628" rel="noreferrer">Demo</a>

blocks|key|2845912|text|您可以使用constexpr函数。下面是C%2B%2B14的方式：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2845913|constexpr+bool+equal(+char+const*+lhs,+char+const*+rhs+)
{
++++while+(*lhs+%7C%7C+*rhs)
++++++++if+(*lhs%2B%2B+!=+*rhs%2B%2B)
++++++++++++return+false;
++++return+true;
}|code-block|syntax|javascript|2845914|演示。|2845915|entityMap|0|LINK|mutability|MUTABLE|url|http://coliru.stacked-crooked.com/a/93c63577777a62ab^0|5|9|0|0|0|2|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

You can use <code>constexpr</code> functions. Here's the C++14 way:

<pre><code>constexpr bool equal( char const* lhs, char const* rhs )
{
 while (*lhs || *rhs)
 if (*lhs++ != *rhs++)
 return false;
 return true;
}
</code></pre>

<a href="http://coliru.stacked-crooked.com/a/93c63577777a62ab" rel="noreferrer">Demo</a>.

blocks|key|2845979|text|这可以在C%2B%2B+11中使用constexpr完成。通过定义递归函数，您可以检查字符串是否相等。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2845980|constexpr+bool+isequal(char+const+*one,+char+const+*two)+
{
++++return+(*one+&&+*two)+?+(*one+==+*two+&&+isequal(one+%2B+1,+two+%2B+1))+:+(!*one+&&+!*two);
}

static_assert(isequal("foo",+"foo"),+"this+should+never+fail");
static_assert(!isequal("foo",+"bar"),+"this+should+never+fail");|code-block|syntax|javascript|2845981|感谢Johannes+Schaub我使用的这段代码，您可以看到完整的所以post+这里|offset|length|2845982|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/5721813/compile-time-assert-for-string-equality^0|0|0|15|2|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]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

This can be done in C++ 11 using constexpr. By defining a recursive function you can check that the string are equal or not. 

<pre><code>constexpr bool isequal(char const *one, char const *two) 
{
 return (*one &amp;&amp; *two) ? (*one == *two &amp;&amp; isequal(one + 1, two + 1)) : (!*one &amp;&amp; !*two);
}

static_assert(isequal("foo", "foo"), "this should never fail");
static_assert(!isequal("foo", "bar"), "this should never fail");
</code></pre>

This code I used thanks to Johannes Schaub and you can see the full SO post <a href="https://stackoverflow.com/questions/5721813/compile-time-assert-for-string-equality">here</a>

blocks|key|1607475|text|这个问题要求提供一种方法来生成关于比较两个字符串的编译时警告。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1607476|但是，如果您需要在C99中使用此方法，则可以在程序尝试运行时生成一个断言错误，但在编译器时会对其进行评估。|1607477|#include+<assert.h>
#include+<string.h>

int+main()+{
++++assert(strcmp("Thing1",+"Thing2")+!=+0);
++++return+0;
}|code-block|syntax|javascript|1607478|现在版本的GCC和Clang将在编译时计算字符串比较，在运行代码时可以看到结果。|1607479|测试工作可以追溯到GCC+4.1.2+(2007)和Clang+3.0.0+(2011)。|1607480|通过使用objdump查看结果，可以看到比较是在编译时完成的：|offset|length|style|CODE|1607481|$+gcc+-Os+-std=c99+static_strcmp_test.c+-o+static_strcmp_test
$+objdump+--disassemble=main+static_strcmp_test
...
0000000000001040+<main>:
++++1040:+++++++f3+0f+1e+fa+++++++++++++endbr64+
++++1044:+++++++31+c0+++++++++++++++++++xor++++%25eax,%25eax
++++1046:+++++++c3++++++++++++++++++++++ret++++|1607482|您也可以在网上试用：https://godbolt.org/z/Kb4GhT99Y|1607483|entityMap|0|LINK|mutability|MUTABLE|url|https://godbolt.org/z/Kb4GhT99Y^0|0|0|0|0|0|4|7|0|0|A|V|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|15|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|17|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|18|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|19|8|@$O|1A|P|1B|Q|R]]|9|@]|A|$]]|$1|S|3|T|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|1D|8|@]|9|@$O|1E|P|1F|1|1G]]|A|$]]|$1|W|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]]|X|$Y|$5|Z|10|11|A|$12|13]]]]

The question asks for a way to generate a compile time warning on comparing two strings.
If you need this to work in C99 however, you can make an assertion error that will raise when the program tries to run, but was evaluated at compiler time.
<pre class="lang-c prettyprint-override"><code>#include &lt;assert.h&gt;
#include &lt;string.h&gt;

int main() {
 assert(strcmp(&quot;Thing1&quot;, &quot;Thing2&quot;) != 0);
 return 0;
}
</code></pre>
Modern versions of GCC and Clang will evaluate the string comparison at compile time, and the results can be seen when the code is run.
Tested this works as far back as GCC 4.1.2 (2007) and Clang 3.0.0 (2011).
You can see the comparison is done at compile time by using <code>objdump</code> to see the results:
<pre><code>$ gcc -Os -std=c99 static_strcmp_test.c -o static_strcmp_test
$ objdump --disassemble=main static_strcmp_test
...
0000000000001040 &lt;main&gt;:
 1040: f3 0f 1e fa endbr64 
 1044: 31 c0 xor %eax,%eax
 1046: c3 ret 
</code></pre>
You can also try it online here: <a href="https://godbolt.org/z/Kb4GhT99Y" rel="nofollow noreferrer">https://godbolt.org/z/Kb4GhT99Y</a>

I would like to create a macro which can compare 2 strings, and emit a compile time error if the condition isn't met. This could be though of as a compile time assertion.

I'm not sure how I could do this.

For instance:

<pre><code>STATIC_COMPARE("THIS STRING","THIS STRING") -&gt; would emit a compile time error
STATIC_COMPARE("THIS STRING","THIS OTHER STRING) -&gt; wouldn't emit a compile time error.
</code></pre>

The macro would look something like

<pre><code>#define STATIC_COMPARE(str1,str2) if (str1==str2) emit an error with a message
</code></pre>

So I guess the question boils down to being able to compare the 2 strings at compile time.

How can you compare two character strings statically at compile time

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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我想要创建一个宏，它可以比较两个字符串，并在不满足条件的情况下发出编译时错误。这可以看作是编译时断言。我不知道我怎么能做到。例如：STATIC_COMPARE("THIS STRING","THIS STRING") -> would emit a compile time errorSTATIC_COMPARE("THIS STRING","THIS OTHER STRING) -> would

问如何在编译时静态地比较两个字符串？
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