原来#define 也可以写成# define的,里面有个看不懂的地方
# define ENTRY(fcn) traceEntry (__FILE__, __LINE__, #fcn)
~~~这里加#是干什么的
谢谢了
[解决办法]
串化 .... 比如 ENTRY(1+2) 被替换成 traceEntry (__FILE__, __LINE__, "1+2 " )
[解决办法]
#x 替换时自动在两边加上引号
##x 替换时自动将内容和周围连接起来，如：
#define A(x,y) x##y
A(o,k) -> ok
[解决办法]
C/C++ Preprocessor Reference
Stringizing Operator (#)
Token-Pasting Operator (##)
Charizing Operator (#@)
[解决办法]
c primier里面讲的比较清楚
[解决办法]
强烈建议你看MSDN。。。
Stringizing Operator (#)
#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 " );
}
Such invocations would be expanded during preprocessing, producing the following code:
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 " );
}
When the program is run, screen output for each line is as follows:
In quotes in the printf function call
"In quotes when printed to the screen "
"This: \ " prints an escaped double quotation mark "
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
Token-Pasting Operator (##)
#define paster( n ) printf( "token " #n " = %d ", token##n )
int token9 = 9;
If a macro is called with a numeric argument like
paster( 9 );
the macro yields
printf( "token " "9 " " = %d ", token9 );
which becomes
printf( "token9 = %d ", token9 );
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
Charizing Operator (#@)
#define makechar(x) #@x
causes the statement
a = makechar(b);
to be expanded to
a = 'b ';
The single-quotation character cannot be used with the charizing operator.
