c/c++中#号的用法

第一种情况作为Stringizing Operator(#)，暂叫字符串化吧。

#define stringer( x ) printf( #x "\n" ) int main() { stringer( In quotes in the printf function call\n ); stringer( "In quotes when printed to the screen"\n ); stringer( "This: \" prints an escaped double quote" ); }

如此的定义在进行处理时将被转换为如下代码：

int main() { printf( "In quotes in the printf function call\n" "\n" ); printf( "\"In quotes when printed to the screen\"\n" "\n" ); printf( "\"This: \\\" prints an escaped double quote\"" "\n" ); }程序运行结果如下：In quotes in the printf function call "In quotes when printed to the screen" "This: \" prints an escaped double quotation mark"

第二种情况作为Charizing Operator(#@)，就叫字符化吧。

例子：

#define makechar(x) #@x

causes the statement

a = makechar(b);

这条语句将被扩展为

a = 'b';注意单引号字符不能使用这样的字符化。

第三种情况作为Token-Pasting Opertor(##)，叫做连接符吧，大概是这样的意思。例子：#define paster( n ) printf( "token" #n " = %d", token##n ) int token9 = 9;

如果一个数字作为此宏的参数调用的话，

paster( 9 );

宏被展开为

printf( "token" "9" " = %d", token9 );

进而成为这样的语句：printf( "token9 = %d", token9 );