C++为了兼容C,默认使iostream与stdio关联,使cin与scanf、cout和printf保持同步,保证混用过程中文件指针不混乱。
此方式会造成性能损失,导致使用cin/cout效率远远低于使用scanf/printf。若保证程序只是用一套指令,可取消同步:
std::ios::sync_with_stdio(false);
取消后使用cin/cout速度有明显提升,但注意不要混用iostream与stdio
std::cin.tie(0);
C++98:In terms of static initialization order, cin is guaranteed to be properly constructed and initialized no later than the first time an object of type ios_base::Init is constructed.
C++11:In terms of static initialization order, cin is guaranteed to be properly constructed and initialized no later than the first time an object of type ios_base::Init is constructed, with the inclusion of <iostream> counting as at least one initialization of such objects with static duration.
cin is tied to the standard output stream cout (see ios::tie), which indicates that cout‘s buffer is flushed (see ostream::flush) before each i/o operation performed on cin.
(来源:http://www.cplusplus.com/reference/iostream/cin/ 网址)
当传入参数为0时,实现cin与cout独立运行,不会等待,提高cin速度
全局域的通过静态常量初始化一个lambda的方式实现对此代码的优先调用
static const int _ = []() { ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); return 0; }();
最新评论
pytz 不对,不要用那个。
我的WordPress没有设置 -p ,Nginx设置了link,但是访问的时候显示找不到wp的服务器IP地址,这是怎么回事儿啊?
是普及运用还是往研究方向。此文从我个人角度可以理解及消化,但更期待如何理解并实践的深入指引。可申请版权型的总结实践指引哦。
请问博主,这些书你都会看吗
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eee
LIBS += -LD:/my_program_design/dll_test/test_library_by_header/ -llibrary,不明白
Спасибо за информацию!!!!!