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ios::sync_with_stdio(false)提高C++读写速度

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

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