有什么标准规定应该输出什么？
例如这个代码：
#include <stdio.h> #include <math.h> int main(int argc,char** argv) { float a = INFINITY; float b = -INFINITY; float c = NAN; printf("float %f %f %f\n",a,b,c); printf("int %d %d %d\n",(int) a,(int) b,(int) c); printf("uint %u %u %u\n",(unsigned int) a,(unsigned int) b,(unsigned int) c); printf("lint %ld %ld %ld\n",(long int) a,(long int) b,(long int) b); printf("luint %lu %lu %lu\n",(unsigned long int) a,(unsigned long int) b,(unsigned long int) c); return 0; }
编译在gcc 4.2.1版(Apple Inc. build 5664)目标：i686-apple-darwin10
输出：
$gcc test.c && ./a.out float inf -inf nan int -2147483648 -2147483648 -2147483648 uint 0 0 0 lint -9223372036854775808 -9223372036854775808 -9223372036854775808 luint 0 9223372036854775808 9223372036854775808
这是很奇怪的(int)inf < 0！？
解决方法
正如保罗所说,这是不明确的：
从§6.3.1.4：
6.3.1.4 Real floating and integer
When a finite value of real floating type is
converted to an integer type other
than _Bool,the fractional part is
discarded (i.e.,the value is
truncated toward zero). If the value
of the integral part cannot be
represented by the integer type,the
behavior is undefined.50)
无穷大不是有限的,整体部分不能以积分形式表示,所以它是未定义的.
