查了下man round
The round functions will return a rounded integer in the specified format that will be rounded to the nearest integer regardless of the current rounding mode.
会向最近的整数舍入，但是没有提.5离左右的两个整数距离一样时如何舍入。
查了下gcc的文档：
Without any explicit options, GCC assumes round to nearest or even and does not care about signalling NaNs. Compare with C99's #pragma STDC FENV ACCESS OFF。
意思是向偶数方向舍入。但是如下代码，测试结果表明，都是进行了四舍五入。
请问这是怎么回事，谢谢；）
printf("0.5 %f\n", round(0.5));
printf("1.5 %f\n", round(1.5));
printf("2.5 %f\n", round(2.5));
printf("3.5 %f\n", round(3.5));
printf("4.5 %f\n", round(4.5));
printf("5.5 %f\n", round(5.5));
printf("6.5 %f\n", round(6.5));
printf("7.5 %f\n", round(7.5));
printf("8.5 %f\n", round(8.5));
printf("9.5 %f\n", round(9.5));
