blocks|key|735257|text|你不能以你想要的方式使用fprintf()。欢迎来到C。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|735258|C%2B%2B+I/O流运算符是类型安全的，并使用运算符重载来实现其魔力。这在C中是不可用的，所以你必须坚持使用不安全的格式化字符串方法。|735259|entityMap^0|C|9|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|N|8|@]|D|@]|E|$]]]|I|$]]

You can't use <code>fprintf()</code> in the way you want. Welcome to C.

C++ I/O stream operators are typesafe and use operator overloading to achieve their magic. That's not available in C so you have to stick to unsafe format string approaches.

blocks|key|735327|text|原则上，你不能，因为C没有重载机制。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|735328|但是，您可以定义许多宏，如下所示：|735329|#define+DEBUG_INT(x)++fprintf(stderr,+"%25d\n",+(x))
#define+DEBUG_CHAR(x)+fprintf(stderr,+"%25c\n",+(x))|code-block|syntax|javascript|735330|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

In principle, you can't, as C don't have an overloading mechanism.

You can, however, define a number of macros like:

<pre><code>#define DEBUG_INT(x) fprintf(stderr, "%d\n", (x))
#define DEBUG_CHAR(x) fprintf(stderr, "%c\n", (x))
</code></pre>

blocks|key|951489|text|没有办法摆脱转换规范，但是如果您使用的是C99编译器，则可以使用__VA_ARGS__并使其更容易一些，例如，在|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|951490|#include+<stdio.h>

#define+DEBUG(fmt,+...)+fprintf(stderr,+(fmt),+__VA_ARGS__)

int+main(void)+{
++int+foo+=+42;
++char+*t+=+"foobar";
++DEBUG("%25s:%25d\n",+t,+foo);
++return+0;
}|code-block|syntax|javascript|951491|entityMap^0|W|B|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

There is no way to get rid of the conversion specifications, but if you have a C99 compiler, you can use <code>__VA_ARGS__</code> and make it a little easier, as, for example, in

<pre><code>#include &lt;stdio.h&gt;

#define DEBUG(fmt, ...) fprintf(stderr, (fmt), __VA_ARGS__)

int main(void) {
 int foo = 42;
 char *t = "foobar";
 DEBUG("%s:%d\n", t, foo);
 return 0;
}
</code></pre>

blocks|key|951526|text|您可以使用GNU+C+Language+Extensions：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|951527|#define+DEBUG(x)+++++++++++++++++++++++++++++++++++++++++++++++++\
++({+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++\
++++if+(__builtin_types_compatible_p+(typeof+(x),+int))++++++++++\
++++++++fprintf(stderr,"%25d\n",x);++++++++++++++++++++++++++++++++\
++++else+if+(__builtin_types_compatible_p+(typeof+(x),+char))++++\
++++++++fprintf(stderr,"%25c\n",x);++++++++++++++++++++++++++++++++\
++++else+if+(__builtin_types_compatible_p+(typeof+(x),+char[]))++\
++++++++fprintf(stderr,"%25s\n",x);++++++++++++++++++++++++++++++++\
++++else+++++++++++++++++++++++++++++++++++++++++++++++++++++++++\
++++++++fprintf(stderr,"unknown+type\n");++++++++++++++++++++++++\

++})|code-block|syntax|javascript|951528|这些都很好：|951529|DEBUG("hello");+//prints+hello
DEBUG(11110);+++//prints+11110+|951530|但是对于字符，你应该将它与lvalue一起使用，否则它的类型将是"int“：|951531|char+c='A';
DEBUG(c);++++//+prints+A
DEBUG('A');++//+prints+65|951532|entityMap|0|LINK|mutability|MUTABLE|url|http://tigcc.ticalc.org/doc/gnuexts.html^0|5|P|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]]]

You can use <a href="http://tigcc.ticalc.org/doc/gnuexts.html" rel="nofollow">GNU C Language Extensions</a> :

<pre><code>#define DEBUG(x) \
 ({ \
 if (__builtin_types_compatible_p (typeof (x), int)) \
 fprintf(stderr,"%d\n",x); \
 else if (__builtin_types_compatible_p (typeof (x), char)) \
 fprintf(stderr,"%c\n",x); \
 else if (__builtin_types_compatible_p (typeof (x), char[])) \
 fprintf(stderr,"%s\n",x); \
 else \
 fprintf(stderr,"unknown type\n"); \

 })
</code></pre>

These are fine:

<pre><code>DEBUG("hello"); //prints hello
DEBUG(11110); //prints 11110 
</code></pre>

But for chars, you should use it with lvalue, otherwise its type will be "int" :

<pre><code>char c='A';
DEBUG(c); // prints A
DEBUG('A'); // prints 65
</code></pre>

blocks|key|735552|text|在C中，您不能可靠地确定对象的类型。因此，你必须引入一些机制来支持泛型编程，例如，将所有对象包含在一个包含类型信息的结构中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|735553|enum+{type_int,+type_double,+type_string,+/*+...+*/+}+type_t;
struct+{
++++++++type_t+type;
++++++++void+*obj;
}+generic_type;|code-block|syntax|javascript|735554|现在，您可以切换到((generic_type)my_object).type。这可能不是你要找的东西。|offset|length|style|CODE|735555|但是，有一个简单的技巧可以判断宏参数是字符串还是其他值。使用宏引号符'#'，您可以将宏参数转换为字符串：|735556|#define+DEBUG(x)+if+(#x[0]+==+'"')+printf("%25s\n",+x);+else+printf("%25d\n",+x)|735557|现在，您可以执行以下操作：|735558|DEBUG("foo+bar");++//+prints+"foo+bar"
DEBUG(23);+++++++++//+prints+"23"|735559|缺点是，这不会让你区分ints和floats。此外，指向字符的指针不会被识别为字符串：|735560|char+*foo+=+"bar";
DEBUG(foo);++++++++//+prints+the+value+of+foo,+not+the+string+pointed+to+by+foo

double+salary;
DEBUG(salary);+++++//+prints+(int)salary,+not+(double)salary|735561|在某些机器上，sizeof(double)+!=+sizeof(int)。这可能有助于进一步区分不同类型的宏参数，但它肯定是不可移植的。|735562|一般来说，如果不在维护可移植性的同时提供泛型编程支持，您将无法完全解决这个问题。|735563|我的建议是:简单地习惯于格式化说明符。|735564|entityMap^0|0|0|9|U|0|0|0|0|0|B|3|G|5|0|0|7|T|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|18|8|@$I|19|J|1A|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|1B|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|1C|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1E|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|1F|8|@$I|1G|J|1H|K|L]|$I|1I|J|1J|K|L]]|9|@]|A|$]]|$1|W|3|X|5|D|7|1K|8|@]|9|@]|A|$E|F]]|$1|Y|3|Z|5|6|7|1L|8|@$I|1M|J|1N|K|L]]|9|@]|A|$]]|$1|10|3|11|5|6|7|1O|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1P|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1Q|8|@]|9|@]|A|$]]]|15|$]]

In C, you cannot reliably determine the type of an object. Hence, you'd have to introduce some mechanism to support generic programming, e.g. enclosing all objects in a structure which holds type information:

<pre><code>enum {type_int, type_double, type_string, /* ... */ } type_t;
struct {
 type_t type;
 void *obj;
} generic_type;
</code></pre>

Now, you can switch over <code>((generic_type)my_object).type</code>. This is probably not what you're looking for.

 
 
However, there's a simple trick to tell whether a macro argument is a string literal or something else. With the macro quoting character '#', you can turn a macro argument into a string:

<pre><code>#define DEBUG(x) if (#x[0] == '"') printf("%s\n", x); else printf("%d\n", x)
</code></pre>

Now you can do the following:

<pre><code>DEBUG("foo bar"); // prints "foo bar"
DEBUG(23); // prints "23"
</code></pre>

On the downside, this won't let you distinguish between e.g.<code>int</code>s and <code>float</code>s. Furthermore, pointers-to-char are not recognized as strings:

<pre><code>char *foo = "bar";
DEBUG(foo); // prints the value of foo, not the string pointed to by foo

double salary;
DEBUG(salary); // prints (int)salary, not (double)salary
</code></pre>

On some machines, <code>sizeof(double) != sizeof(int)</code>. This might help to further distinguish between the different types of your macro arguments, but it's certainly not portable.

 
 
Generally speaking, you won't be able to completely solve this problem without some serious effort towards generic programming support while also maintaining portability.

My advice: simply get used to format specifiers.

blocks|key|735613|text|您可以简单地执行以下操作，而不是使用__VA_ARGS__：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|735614|#define+DEBUG(x...)+fprintf(stderr,+x)|code-block|syntax|javascript|735615|与GCC内置的方法不同，此方法允许您混合匹配-您可以打印"string="，而不是一次只打印一种类型。这样也不会遇到大小和类型不兼容的问题--它本质上与fprintf相同，除了可以在构建时被排除之外！|735616|entityMap^0|I|B|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Instead of using the <code>__VA_ARGS__</code>, you can just simply do the following:

<pre><code>#define DEBUG(x...) fprintf(stderr, x)
</code></pre>

Unlike the GCC built-in methods, this method allows you to mix-and-match - you can print "string=", instead of just one type at a time. You also won't run into size and type incompatibility this way - it's essentially the same as fprintf, except able to be excluded at build-time!

In C++, having

<pre><code>#define DEBUG(A) cerr &lt;&lt; (A) &lt;&lt; endl;
</code></pre>

I can send anything to it, and it can print it. However, in C, I must specify its type with %d, %c or %s etc. But I don't want to write its type all time, I want to use <code>fprintf</code> like <code>cerr</code>. How can I do that?

For example: in C

<pre><code>#define DEBUG(A) X // X is what I want to write 
...
// in function, when I put
DEBUG(5); // I just want to print 5 
// or, with same statement, when I say 
DEBUG('a'); // output : a
</code></pre>

How can I print values in C without specifying their types, like done with "cerr << (A) << endl" in C++?

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在C++中，有#define DEBUG(A) cerr << (A) << endl;我可以向它发送任何东西，它也可以打印出来。然而，在C中，我必须用%d，%c或%s等来指定它的类型。但我不想一直写它的类型，我想像cerr一样使用fprintf。我该怎么做呢？例如:在C中#define DEBUG(A) X // X...

问如何在不指定类型的情况下用C打印值，就像C++中的"cerr << (A) << endl“一样？
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问如何在不指定类型的情况下用C打印值，就像C++中的"cerr << (A) << endl“一样？EN

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问如何在不指定类型的情况下用C打印值，就像C++中的"cerr << (A) << endl“一样？
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