C99 | double trunc (double x);
float truncf (float x); long double truncl (long double x); |
C++11 | double trunc (double x);
float trunc (float x); long double trunc (long double x); double trunc (T x); // additional overloads for integral types |
C99 | 头文件<tgmath.h> 提供了该函数的类型泛型宏版本。 |
C++11 | 这个头文件(<cmath>)为整型提供了额外的重载:
这些重载有效地在计算之前将x转换为double(在T是任何整型时定义)。
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/* round vs floor vs ceil vs trunc */ #include <stdio.h> /* printf */ #include <math.h> /* round, floor, ceil, trunc */ int main () { const char * format = "%.1f \t%.1f \t%.1f \t%.1f \t%.1f\n"; printf ("value\tround\tfloor\tceil\ttrunc\n"); printf ("-----\t-----\t-----\t----\t-----\n"); printf (format, 2.3,round( 2.3),floor( 2.3),ceil( 2.3),trunc( 2.3)); printf (format, 3.8,round( 3.8),floor( 3.8),ceil( 3.8),trunc( 3.8)); printf (format, 5.5,round( 5.5),floor( 5.5),ceil( 5.5),trunc( 5.5)); printf (format,-2.3,round(-2.3),floor(-2.3),ceil(-2.3),trunc(-2.3)); printf (format,-3.8,round(-3.8),floor(-3.8),ceil(-3.8),trunc(-3.8)); printf (format,-5.5,round(-5.5),floor(-5.5),ceil(-5.5),trunc(-5.5)); return 0; } |
value round floor ceil trunc ----- ----- ----- ---- ----- 2.3 2.0 2.0 3.0 2.0 3.8 4.0 3.0 4.0 3.0 5.5 6.0 5.0 6.0 5.0 -2.3 -2.0 -3.0 -2.0 -2.0 -3.8 -4.0 -4.0 -3.0 -3.0 -5.5 -6.0 -6.0 -5.0 -5.0 |
floor | 向下舍入(function ) |
ceil | 向上舍入(function ) |
round | 就近舍入(function ) |
rint | 舍入到整数值(function ) |