do...while(0)的作用
1. 消除代码的冗余以及无需使用goto语句。
int* p = new int;
bool bOK(true);
bool bOK(true);
do{
bOK = func1();
if(!bOK) break;
bOK = func2();
if(!bOK) break;
//...
}while(0);
delete p;
p = NULL;
2. 宏定义中的do...while(0)避免悬空else分支导致编译失败或运行错误如:
#define safe_delete(p) do{ delete p; p = NULL;}while(0)
if (p != NULL)
safe_delete(p);
else
do...sth...
if (p != NULL)
safe_delete(p);
else
do...sth...
(1)如果去掉do...while(0)则会导致else无对应的if语句,导致编译错误。
(2)假设无else语句,则宏定义中的第二句将永远执行,导致意想不到的结果
3. 免去空语句出现编译告警。
In older compilers, this was necessary to prevent the compiler from issuing a warning. For example:
#define do_nothing do {} while (0)
The current gcc compiler provides another method that can be used in place of the do-loop idiom as shown in the following example.
#define foo ({ \
statement_1; \
statement_2; \
})
posted on 2013-06-30 19:44 eric.geoffrey 阅读(197) 评论(0) 编辑 收藏 举报