blocks|key|2079544|text|您可能对protocol+buffers和其他IDL方案感兴趣。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2079545|entityMap|0|LINK|mutability|MUTABLE|url|http://code.google.com/apis/protocolbuffers/docs/overview.html^0|4|G|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You might be interested in <a href="http://code.google.com/apis/protocolbuffers/docs/overview.html" rel="nofollow">protocol buffers</a> and other IDL schemes.

blocks|key|1330970|text|对于这个问题，我所见过的最优雅的解决方案是Sean+Barrett的writefv，它用在他的小型图像写入库stb_image_write+available+here中。他只实现了几个原语(没有错误处理)，但同样的方法可以扩展到基本上是二进制printf+(对于读取，您可以执行相同的操作来获得二进制scanf)。非常优雅和整洁！事实上，整个事情是如此简单，我不妨把它包含在这里：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1330971|static+void+writefv(FILE+*f,+const+char+*fmt,+va_list+v)
{
+++while+(*fmt)+{
++++++switch+(*fmt%2B%2B)+{
+++++++++case+'+':+break;
+++++++++case+'1':+{+unsigned+char+x+=+(unsigned+char)+va_arg(v,+int);+fputc(x,f);+break;+}
+++++++++case+'2':+{+int+x+=+va_arg(v,int);+unsigned+char+b[2];
+++++++++++++++++++++b[0]+=+(unsigned+char)+x;+b[1]+=+(unsigned+char)+(x>>8);
+++++++++++++++++++++fwrite(b,2,1,f);+break;+}
+++++++++case+'4':+{+stbiw_uint32+x+=+va_arg(v,int);+unsigned+char+b[4];
+++++++++++++++++++++b[0]=(unsigned+char)x;+b[1]=(unsigned+char)(x>>8);
+++++++++++++++++++++b[2]=(unsigned+char)(x>>16);+b[3]=(unsigned+char)(x>>24);
+++++++++++++++++++++fwrite(b,4,1,f);+break;+}
+++++++++default:
++++++++++++assert(0);
++++++++++++return;
++++++}
+++}
}|code-block|syntax|javascript|1330972|下面是他如何使用它来编写真彩色.BMP文件：|1330973|static+int+outfile(char+const+*filename,+int+rgb_dir,+int+vdir,+int+x,+int+y,+int+comp,+void+*data,+int+alpha,+int+pad,+const+char+*fmt,+...)
{
+++FILE+*f;
+++if+(y+<+0+%7C%7C+x+<+0)+return+0;
+++f+=+fopen(filename,+"wb");
+++if+(f)+{
++++++va_list+v;
++++++va_start(v,+fmt);
++++++writefv(f,+fmt,+v);
++++++va_end(v);
++++++write_pixels(f,rgb_dir,vdir,x,y,comp,data,alpha,pad);
++++++fclose(f);
+++}
+++return+f+!=+NULL;
}

int+stbi_write_bmp(char+const+*filename,+int+x,+int+y,+int+comp,+const+void+*data)
{
+++int+pad+=+(-x*3)+&+3;
+++return+outfile(filename,-1,-1,x,y,comp,(void+*)+data,0,pad,
+++++++++++"11+4+22+4"+"4+44+22+444444",
+++++++++++'B',+'M',+14%2B40%2B(x*3%2Bpad)*y,+0,0,+14%2B40,++//+file+header
++++++++++++40,+x,y,+1,24,+0,0,0,0,0,0);+++++++++++++//+bitmap+header
}|1330974|(省略了write_pixels的定义，因为它在这里非常切线)|1330975|entityMap|0|LINK|mutability|MUTABLE|url|http://nothings.org/stb/stb_image_write.h^0|Y|7|1I|F|3E|6|47|5|28|4|0|0|0|0|0|4|C|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|F|3|G|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1B|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

The most elegant solution I've seen for this problem yet is Sean Barrett's <code>writefv</code>, used in his tiny image-writing library <code>stb_image_write</code> available <a href="http://nothings.org/stb/stb_image_write.h" rel="nofollow">here</a>. He only implements a few primitives (and no error handling), but the same approach can be extended to what is basically a binary <code>printf</code> (and for reading, you can do the same to get a binary <code>scanf</code>). Very elegant and tidy! In fact, the whole thing is so simple, I might as well include it here:

<pre><code>static void writefv(FILE *f, const char *fmt, va_list v)
{
 while (*fmt) {
 switch (*fmt++) {
 case ' ': break;
 case '1': { unsigned char x = (unsigned char) va_arg(v, int); fputc(x,f); break; }
 case '2': { int x = va_arg(v,int); unsigned char b[2];
 b[0] = (unsigned char) x; b[1] = (unsigned char) (x&gt;&gt;8);
 fwrite(b,2,1,f); break; }
 case '4': { stbiw_uint32 x = va_arg(v,int); unsigned char b[4];
 b[0]=(unsigned char)x; b[1]=(unsigned char)(x&gt;&gt;8);
 b[2]=(unsigned char)(x&gt;&gt;16); b[3]=(unsigned char)(x&gt;&gt;24);
 fwrite(b,4,1,f); break; }
 default:
 assert(0);
 return;
 }
 }
}
</code></pre>

and here is how he writes truecolor .BMP files using it:

<pre><code>static int outfile(char const *filename, int rgb_dir, int vdir, int x, int y, int comp, void *data, int alpha, int pad, const char *fmt, ...)
{
 FILE *f;
 if (y &lt; 0 || x &lt; 0) return 0;
 f = fopen(filename, "wb");
 if (f) {
 va_list v;
 va_start(v, fmt);
 writefv(f, fmt, v);
 va_end(v);
 write_pixels(f,rgb_dir,vdir,x,y,comp,data,alpha,pad);
 fclose(f);
 }
 return f != NULL;
}

int stbi_write_bmp(char const *filename, int x, int y, int comp, const void *data)
{
 int pad = (-x*3) &amp; 3;
 return outfile(filename,-1,-1,x,y,comp,(void *) data,0,pad,
 "11 4 22 4" "4 44 22 444444",
 'B', 'M', 14+40+(x*3+pad)*y, 0,0, 14+40, // file header
 40, x,y, 1,24, 0,0,0,0,0,0); // bitmap header
}
</code></pre>

(definition of <code>write_pixels</code> elided since it's pretty tangential here)

blocks|key|2075181|text|我可以通过对代码进行一些重构，让它看起来不那么难看，这样复杂的数据结构就可以通过对其底层类型的一系列调用来读取。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2075182|我假设您的代码是纯C语言，而不是C%2B%2B，因为在后者中，您可能会抛出异常，而不是使用goto语句。|2075183|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

I would make your code less inelegant looking by refactoring it out a bit, so your complex data structures are read with a series of calls of its underlying types.

I assume your code is pure C and not C++ because in the latter you would probably throw exceptions rather than using goto statements.

blocks|key|1330998|text|如果要反序列化二进制数据，一种选择是为要使用的结构定义序列化宏。在使用模板函数和流的C%2B%2B中，这要容易得多。(boost::serialization是一个非侵入式的序列化库，但如果您想要进行侵入式的序列化，您可以让它更优雅)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1330999|简单的C语言宏：|1331000|#define+INT(f,v)+\
++{+int+_t;+fread(&_t,+sizeof(int),+1,+f);+v+=+ntohl(_t);+}
#define+FLOAT(f,v)+\
++{+int+_t;+fread(&_t,+sizeof(int),+1,+f);+v+=+ntohl(_t);+/*+type+punning+*/+memcpy(&v,+&_t,+sizeof(float));+}
...|code-block|syntax|javascript|1331001|用法：|1331002|++int+a;
++float+b;
++FILE+*f+=+fopen("file",+"rb");

++INT(f,+a);
++FLOAT(f,+b);|1331003|是的，序列化代码是编写起来最无聊、最愚蠢的代码之一。如果可以，使用元数据描述您的数据结构，并机械地生成代码。有一些工具和库可以帮助实现这一点，您也可以使用Perl、Python、PowerShell或其他语言编写自己的库。|1331004|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

If you want to de-serialize binary data, one option is to define serialization macros for the structs that you want to use. This is a lot easier in C++ with template functions and streams. (boost::serialization is a non-intrusive serialization library, but if you want to go intrusive, you can make it more elegant)

Simple C macros:

<pre><code>#define INT(f,v) \
 { int _t; fread(&amp;_t, sizeof(int), 1, f); v = ntohl(_t); }
#define FLOAT(f,v) \
 { int _t; fread(&amp;_t, sizeof(int), 1, f); v = ntohl(_t); /* type punning */ memcpy(&amp;v, &amp;_t, sizeof(float)); }
...
</code></pre>

Usage:

<pre><code> int a;
 float b;
 FILE *f = fopen("file", "rb");

 INT(f, a);
 FLOAT(f, b);
</code></pre>

And, yes, serialization code is some of the most boring and brain-dead code to write. If you can, describe your data structures using metadata, and generate the code mechanically instead. There are tools and libs to help with this, or you can roll your own in Perl or Python or PowerShell or whatever.

blocks|key|1331022|text|数组读取部分看起来应该有自己的可重用函数。除此之外，如果您确实有可用的C%2B%2B+(从问题中并不完全清楚)，那么硬编码变量的大小是不必要的，因为可以从指针中推断出大小。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1331023|template<typename+T>
bool+read(+FILE*+const+f,+T*+const+p,+size_t+const+n+=+1+)
{
+++++return+n+*+sizeof(T)+==+fread(f,+sizeof+T,+n,+p);
}

template<typename+T>
bool+read(+FILE*+const+f,+T&+result+)
{
+++++return+read(f,+&result);
}

template<typename+Tcount,+typename+Telement>
bool+read_counted_array(+FILE*+const+f,+Tcount&+n,+Telement*&+p+)
{
+++++if+(!read(f,+n)+%7C%7C+!(p+=+new+Telement[n]))
+++++++++return+false;
+++++if+(read(f,+p,+n))
+++++++++return+true;
+++++delete[]+p;
+++++p+=+0;
+++++return+false;
}|code-block|syntax|javascript|1331024|然后|1331025|uint32_t+type,+k;
uint32_t+*variable;
FILE+*f;

if+(read(f,+type)+&&
++++read_counted_array(f,+k,+variable)+&&+...
+++)+{
+++//...
}
else
++++goto+boundsError;|1331026|当然，如果数据被传递给假定使用了malloc的代码，那么您可以继续使用malloc和free，而不是new[]和delete[]。|offset|length|style|CODE|1331027|entityMap^0|0|0|0|0|G|6|Z|6|16|4|1E|5|1K|8|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]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]|$M|Z|N|10|O|P]|$M|11|N|12|O|P]|$M|13|N|14|O|P]|$M|15|N|16|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$]]

The array-reading part looks like it deserves its own reusable function. Beyond that, if you do actually have C++ available (it isn't completely clear from the question), then hard-coding the size of variables is unnecessary, as the size can be deduced from the pointer.

<pre><code>template&lt;typename T&gt;
bool read( FILE* const f, T* const p, size_t const n = 1 )
{
 return n * sizeof(T) == fread(f, sizeof T, n, p);
}

template&lt;typename T&gt;
bool read( FILE* const f, T&amp; result )
{
 return read(f, &amp;result);
}

template&lt;typename Tcount, typename Telement&gt;
bool read_counted_array( FILE* const f, Tcount&amp; n, Telement*&amp; p )
{
 if (!read(f, n) || !(p = new Telement[n]))
 return false;
 if (read(f, p, n))
 return true;
 delete[] p;
 p = 0;
 return false;
}
</code></pre>

and then

<pre><code>uint32_t type, k;
uint32_t *variable;
FILE *f;

if (read(f, type) &amp;&amp;
 read_counted_array(f, k, variable) &amp;&amp; ...
 ) {
 //...
}
else
 goto boundsError;
</code></pre>

Of course, feel free to continue using <code>malloc</code> and <code>free</code> instead of <code>new[]</code> and <code>delete[]</code> if the data is being handed off to code that assume that <code>malloc</code> was used.

blocks|key|5038221|text|下面是我想出来的一些C99代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5038222|5038223|read_values.h，read_values.c|unordered-list-item|offset|length|5038224|read_array.h，read_array.c|5038225|5038226|您的示例应为：|5038227|#include+"read_values.h"
#include+"read_array.h"

assert(sizeof+(uint32_t)+==+4);

uint32_t+type,+k;
uint32_t+*variable;
FILE+*f;

_Bool+success+=
++++read_values(f,+"c4c4",+&type,+&k)+&&
++++read_array(f,+variable,+k);

if(!success)
{
++++/*+...+*/
}|code-block|syntax|javascript|5038228|entityMap|0|LINK|mutability|MUTABLE|url|http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_values.h|1|http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_values.c|2|http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_array.h|3|http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_array.c^0|0|0|0|D|0|E|D|1|0|0|C|2|D|C|3|0|0|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|17|8|@]|9|@$F|18|G|19|1|1A]|$F|1B|G|1C|1|1D]]|A|$]]|$1|H|3|I|5|E|7|1E|8|@]|9|@$F|1F|G|1G|1|1H]|$F|1I|G|1J|1|1K]]|A|$]]|$1|J|3|-4|5|6|7|1L|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1M|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|1N|8|@]|9|@]|A|$P|Q]]|$1|R|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|S|$T|$5|U|V|W|A|$X|Y]]|Z|$5|U|V|W|A|$X|10]]|11|$5|U|V|W|A|$X|12]]|13|$5|U|V|W|A|$X|14]]]]

Here's some C99 code I came up with:

<ul>
<li><a href="http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_values.h" rel="nofollow">read_values.h</a>, <a href="http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_values.c" rel="nofollow">read_values.c</a></li>
<li><a href="http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_array.h" rel="nofollow">read_array.h</a>, <a href="http://mercurial.intuxication.org/hg/cstuff/raw-file/tip/read_array.c" rel="nofollow">read_array.c</a></li>
</ul>

Your example would read:

<pre><code>#include "read_values.h"
#include "read_array.h"

assert(sizeof (uint32_t) == 4);

uint32_t type, k;
uint32_t *variable;
FILE *f;

_Bool success =
 read_values(f, "c4c4", &amp;type, &amp;k) &amp;&amp;
 read_array(f, variable, k);

if(!success)
{
 /* ... */
}
</code></pre>

I've been loading a lot of binary files recently using C/C++, and I'm bothered by how inelegant it can be. Either I get a lot of code that looks like this (I've since moved on):

<pre><code>uint32_t type, k;
uint32_t *variable;
FILE *f;

if (!fread(&amp;type, 4, 1, f))
 goto boundsError;

if (!fread(&amp;k, 4, 1, f))
 goto boundsError;

variable = malloc(4 * k);
if (!fread(variable, 4 * k, 1, f))
 goto boundsError;
</code></pre>

Or, I define a local, packed struct so that I can read in constant-sized blocks easier. It seems to me, however, that for such a simple problem—that is, reading a specified file into memory—could be done more efficiently and in more of a readable manner. Does anyone have any tips/tricks etc? I'd like to clarify that I'm not looking for a library or something to handle this; I might be tempted if I were designing my own file and had to change the file spec a lot, but for now I'm just looking for stylistic answers.

Also, some of you might suggest <code>mmap</code>—I love mmap! I use it a lot, but the problem with it is that it leads to nasty code for handling unaligned data types, which doesn't really exist when using stdio. In the end, I'd be writing stdio-like wrapper functions for reading from memory.

Thanks!

EDIT: I should also clarify that I can't change file formats—there's a binary file that I have to read; I can't request the data in another format.

Elegant binary i/o in C?

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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我最近使用C/C++加载了很多二进制文件，我被它是多么的不优雅所困扰。要么我得到了很多看起来像这样的代码(我已经离开了)：uint32_t type, k;uint32_t *variable;FILE *f;if (!fread(&type, 4, 1, f))    goto boundsError;if (!fr...

问C中优雅的二进制i/o？
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问C中优雅的二进制i/o？EN