blocks|key|1147087|text|我太习惯打字了|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1147088|for+(int+i+=+0;+i+<+n;+%2B%2Bi)+{+...+}|code-block|syntax|javascript|1147089|在C%2B%2B中，使用非C99编译器是一件痛苦的事情，我不得不说|1147090|int+i;
for+(i+=+0;+i+<+n;+%2B%2Bi+)+{+...+}|1147091|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|$]]

I'm so used to typing

<pre><code>for (int i = 0; i &lt; n; ++i) { ... }
</code></pre>

in C++ that it's a pain to use a non-C99 compiler where I am forced to say

<pre><code>int i;
for (i = 0; i &lt; n; ++i ) { ... }
</code></pre>

blocks|key|1361987|text|stdint.h，它定义了int8_t、uint8_t等。不再需要对整数的宽度做不可移植的假设。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1361988|uint32_t+truth+=+0xDECAFBAD;|code-block|syntax|javascript|1361989|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Stdint.h^0|0|8|D|6|K|7|0|8|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$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]]|$1|K|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

<a href="http://en.wikipedia.org/wiki/Stdint.h" rel="noreferrer"><code>stdint.h</code></a>, which defines <code>int8_t</code>, <code>uint8_t</code>, etc. No more having to make non-portable assumptions about how wide your integers are.

<pre><code>uint32_t truth = 0xDECAFBAD;
</code></pre>

blocks|key|1362228|text|我认为新的初始化器机制非常重要。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1362229|struct+{+int+x,+y;+}+a[10]+=+{+[3]+=+{+.y+=+12,+.x+=+1+}+};|code-block|syntax|javascript|1362230|好吧-不是一个令人信服的例子，但符号是准确的。您可以初始化数组的特定元素和结构的特定成员。|1362231|也许这是一个更好的例子--尽管我承认它并不是非常令人信服：|1362232|enum+{+Iron+=+26,+Aluminium+=+13,+Beryllium+=+4,+...+};

const+char+*element_names[]+=
{
++++[Iron]++++++=+"Iron",
++++[Aluminium]+=+"Aluminium",
++++[Beryllium]+=+"Beryllium",
++++...
};|1362233|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I think that the new initializer mechanisms are extremely important.

<pre><code>struct { int x, y; } a[10] = { [3] = { .y = 12, .x = 1 } };
</code></pre>

OK - not a compelling example, but the notation is accurate. You can initialize specific elements of an array, and specific members of a structure.

Maybe a better example would be this - though I'd admit it isn't hugely compelling:

<pre><code>enum { Iron = 26, Aluminium = 13, Beryllium = 4, ... };

const char *element_names[] =
{
 [Iron] = "Iron",
 [Aluminium] = "Aluminium",
 [Beryllium] = "Beryllium",
 ...
};
</code></pre>

blocks|key|1361950|text|支持以//开头的单行注释。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1361951|entityMap^0|3|2|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|$]]

Support for one-line comments beginning with <code>//</code>.

blocks|key|1362393|text|可变长度数组：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1362394|int+x;
scanf("%25d",+&x);
int+a[x];
for+(int+i+=+0;+i+<+x;+%2B%2Bi)
++++a[i]+=+i+*+i;
for+(int+i+=+0;+i+<+x;+%2B%2Bi)
++++printf("%25d\n",+a[i]);|code-block|syntax|javascript|1362395|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|$]]

Variable length arrays:

<pre><code>int x;
scanf("%d", &amp;x);
int a[x];
for (int i = 0; i &lt; x; ++i)
 a[i] = i * i;
for (int i = 0; i &lt; x; ++i)
 printf("%d\n", a[i]);
</code></pre>

blocks|key|1362352|text|能够在块的开头以外的位置声明变量。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1362353|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|$]]

Being able to declare variables at locations other than the start of a block.

blocks|key|1362067|text|不同的宏。使生成具有无限数量参数的样板代码变得更容易。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1362068|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|$]]

Variadic macros. Makes it easier to generate boilerplate code with unlimited number of arguments.

blocks|key|1362519|text|snprintf()+-说真的，能够使用安全的格式化字符串是非常有价值的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1362520|entityMap^0|0|A|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|$]]

<code>snprintf()</code> - seriously, it's worth a lot to be able to do safe formatted strings.

blocks|key|1147244|text|复合文字。逐个成员设置结构是so+'89+;)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1147245|您还可以使用它们来获取指向具有自动存储持续时间的对象的指针，而无需声明不必要的变量，例如|1147246|foo(&(int){+4+});|code-block|syntax|javascript|1147247|而不是|1147248|int+tmp+=+4;
foo(&tmp);|1147249|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Compound literals. Setting structures member-by-member is so '89 ;)

You can also use them to get pointers to objects with automatic storage duration without declaring unnecessary variables, eg

<pre><code>foo(&amp;(int){ 4 });
</code></pre>

insteand of

<pre><code>int tmp = 4;
foo(&amp;tmp);
</code></pre>

blocks|key|1147333|text|bool类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1147334|你现在可以这样做了：|1147335|bool+v+=+5;

printf("v=%25u\n",+v);|code-block|syntax|javascript|1147336|将打印|1147337|1|1147338|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

The bool type.

You can now do something like that:

<pre><code>bool v = 5;

printf("v=%u\n", v);
</code></pre>

will print

<pre><code>1
</code></pre>

blocks|key|1147104|text|支持inline函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1147105|entityMap^0|2|6|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|$]]

Support for <code>inline</code> functions.

blocks|key|1362601|text|复合字面量，前面已经提到过，但这是我引人注目的例子：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1362602|struct+A+*a+=+malloc(sizeof(*a));
*a+=+(struct+A){0};++/*+full+zero-initialization+++*/
/*+or+*/
*a+=+(struct+A){.bufsiz=1024,+.fd=2};+++/*+rest+are+zero-initialized.++*/|code-block|syntax|javascript|1362603|这是一种清晰的初始化数据的方法，即使它在堆上。没有办法忘记对某些东西进行零初始化。|1362604|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Compound literals, already mentioned but here's my compelling example:

<pre><code>struct A *a = malloc(sizeof(*a));
*a = (struct A){0}; /* full zero-initialization */
/* or */
*a = (struct A){.bufsiz=1024, .fd=2}; /* rest are zero-initialized. */
</code></pre>

It's a clear way to initialize data even if it's on the heap. There is no way to forget to zero-initialize something.

blocks|key|1362566|text|restrict关键字。尤其是当你处理数字的时候。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1362567|entityMap^0|0|8|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|$]]

The <code>restrict</code> keyword. Especially when you crunch numbers...

blocks|key|1362467|text|Unicode转义序列支持：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1362468|printf("It's+all+\u03B5\u03BB\u03BB\u03B7\u03BD\u03B9\u03BA\u03AC+to+me.\n");|code-block|syntax|javascript|1362469|或者甚至是文字Unicode字符：|1362470|printf("日本語\n");|1362471|(注意:可能不能工作取决于您的语言环境；对不同编码的可移植支持将需要更多的工作)|1362472|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Unicode escape sequence support:

<pre><code>printf("It's all \u03B5\u03BB\u03BB\u03B7\u03BD\u03B9\u03BA\u03AC to me.\n");
</code></pre>

Or even, literal Unicode characters:

<pre><code>printf("日本語\n");
</code></pre>

(note: may not work depending on your locale; portable support for different encodings will take more work than this)

blocks|key|1147452|text|十六进制浮点常量(0x1.8p0f)和转换说明符(%25a、%25A)。如果您经常处理低级别的数字细节，那么与十进制文字和转换相比，这是一个巨大的改进。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1147453|它们使您在为算法指定常量时不必担心四舍五入，并且对于调试低级浮点代码非常有用。|1147454|entityMap^0|9|8|P|2|S|2|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

Hexadecimal floating point constants (<code>0x1.8p0f</code>) and conversion specifiers (<code>%a</code>, <code>%A</code>). If you deal with low-level numerical details frequently, these are an enormous improvement over decimal literals and conversions.

They save you from worries about rounding when specifying constants for an algorithm, and are immensely useful for debugging low-level floating-point code.

blocks|key|1146852|text|就我个人而言，我喜欢承认IEC+60559:1989+(微处理器系统的二进制浮点算法)和更好的浮点支持。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1146853|类似地，设置和查询浮点舍入模式，检查Nan/Infinity/subnormal数字等，都是很棒的。|1146854|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/IEEE_754-2008^0|C|E|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Personally, I like the acknowledgment of <a href="http://en.wikipedia.org/wiki/IEEE_754-2008" rel="noreferrer">IEC 60559:1989</a> (Binary floating-point arithmetic for microprocessor systems) and much better floating-point support.

In a similar vein, setting and querying the floating-point rounding mode, checking for Nan/Infinity/subnormal numbers, etc., is great to have.

<a href="http://en.wikipedia.org/wiki/C99" rel="noreferrer">C99</a> has been around for over 10 years, but support for it has been slow coming, so most developers have stuck with C89. Even today, I'm sometimes mildly surprised when I come across C99 features in C code.

Now that most major compilers support C99 (MSVC being a notable exception, and some embedded compilers also lagging behind), I feel that developers who work with C probably ought to know about what C99 features are available to them. Some of the features are just common features that were never standardized before (<code>snprintf</code>, for instance), or are familiar from C++ (flexible variable declaration placement, or single-line <code>//</code> comments), but some of the new features were first introduced in C99 and are unfamiliar to many programmers.

What do you find the most useful new features in C99?

For reference, <a href="http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf" rel="noreferrer">the C99 standard</a> (labelled as a draft, but identical to the updated standard, as far as I know), the <a href="http://www.open-std.org/jtc1/sc22/wg14/www/newinc9x.htm" rel="noreferrer">list of new features</a>, and the <a href="http://gcc.gnu.org/c99status.html" rel="noreferrer">GCC C99 implementation status</a>.

One feature per answer, please; feel free to leave multiple answers. Short code examples demonstrating new features are encouraged.

What are the most useful new features in C99?

编译器

已经存在超过10年了，但对它的支持来得很慢，所以大多数开发人员都坚持使用C89。即使在今天，当我在C代码中遇到C99特性时，我有时也会感到些许惊讶。现在大多数主流编译器都支持C99 (MSVC是一个明显的例外，一些嵌入式编译器也落后了)，我觉得使用C的开发人员可能应该知道他们可以使用哪些C99特性。其中一些功能只是以前从未标准化过的常见功能(例如snprintf)，或者是C++中熟悉的功能(灵活的

问C99中最有用的新功能是什么？
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回答 16

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