user-0 提问: 判断浮点数相等的问题

回复:
user: user-1
content: 楼主的这种情况在赋值后是区分不了不相等  楼上给的方法都是怎么判断两个浮点数相等  楼主赋值时浮点float本身就没那么多精度，也就是说你数据在赋值时已经不精确了， 所以你的a,b变量在赋值后内存存的都一样  可以使用double，再不行long double，通常是够用了

user: user-2
content: float.h 中有#define FLT_EPSILON                1.19209290E-07F   #include <float.h>;  double a, b;   if( abs(a-b) < FLT_EPSILON) {}  比较误差小于允许的范围就可以了吧

user: user-3
content: if( abs(a-b)>0.000000000000000001)

user: user-4
content: http://bbs.csdn.net/topics/390676437

user: user-2
content: http://blog.csdn.net/sharkw/article/details/1937581

user: user-5
content: 电脑存储的精度问题，只能用误差来比较

user: user-4
content: 仅供参考：#include <stdio.h> #include <stdlib.h> #include <string.h> float f; double d; void showf() {     char bs[65];     char b[65];     unsigned char *p;     char e[12];     char *t;     int ex;      printf("\nf=%.6f\n",f);     p=(unsigned char *)&f;     printf("hex=%02X %02X %02X %02X\n",p[3],p[2],p[1],p[0]);     ltoa(*(long *)&f,b,2);     sprintf(bs,"%032s",b);     printf("bin=%s\n",bs);     printf("bin=%.1s %.8s   %s\n",bs,bs+1,bs+9);     strncpy(e,bs+1,8);e[8]=0;     ex=strtol(e,&t,2);     printf("    %c %-4d-127 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+9);     ex-=127;     printf("    %c %-8d 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+9); } void showd() {     char bs[65];     char b[65];     unsigned char *p;     char e[12];     char *t;     int ex;      printf("\nd=%.15lf\n",d);     p=(unsigned char *)&d;     printf("hex=%02X %02X %02X %02X %02X %02X %02X %02X\n",p[7],p[6],p[5],p[4],p[3],p[2],p[1],p[0]);     _i64toa(*(__int64 *)&d,b,2);     sprintf(bs,"%064s",b);     printf("bin=%s\n",bs);     printf("bin=%.1s %.11s   %s\n",bs,bs+1,bs+12);     strncpy(e,bs+1,11);e[11]=0;     ex=strtol(e,&t,2);     printf("    %c %-6d-1023 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+12);     ex-=1023;     printf("    %c %-11d 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+12); } int main() {      for (f=0.0f;f<=2.2f;f+=0.2f) showf();     printf("------------\n");     f=2.0f;showf();     printf("-----------------------------------\n");     for (d=0.0 ;d<=2.2 ;d+=0.2 ) showd();     printf("------------\n");     d=2.0 ;showd();      return 0; } // //f=0.000000 //hex=00 00 00 00 //bin=00000000000000000000000000000000 //bin=0 00000000   00000000000000000000000 //  + 0   -127 1.00000000000000000000000 //  + -127     1.00000000000000000000000 // //f=0.200000 //hex=3E 4C CC CD //bin=00111110010011001100110011001101 //bin=0 01111100   10011001100110011001101 //  + 124 -127 1.10011001100110011001101 //  + -3       1.10011001100110011001101 // //f=0.400000 //hex=3E CC CC CD //bin=00111110110011001100110011001101 //bin=0 01111101   10011001100110011001101 //  + 125 -127 1.10011001100110011001101 //  + -2       1.10011001100110011001101 // //f=0.600000 //hex=3F 19 99 9A //bin=00111111000110011001100110011010 //bin=0 01111110   00110011001100110011010 //  + 126 -127 1.00110011001100110011010 //  + -1       1.00110011001100110011010 // //f=0.800000 //hex=3F 4C CC CD //bin=00111111010011001100110011001101 //bin=0 01111110   10011001100110011001101 //  + 126 -127 1.10011001100110011001101 //  + -1       1.10011001100110011001101 // //f=1.000000 //hex=3F 80 00 00 //bin=00111111100000000000000000000000 //bin=0 01111111   00000000000000000000000 //  + 127 -127 1.00000000000000000000000 //  + 0        1.00000000000000000000000 // //f=1.200000 //hex=3F 99 99 9A //bin=00111111100110011001100110011010 //bin=0 01111111   00110011001100110011010 //  + 127 -127 1.00110011001100110011010 //  + 0        1.00110011001100110011010 // //f=1.400000 //hex=3F B3 33 34 //bin=00111111101100110011001100110100 //bin=0 01111111   01100110011001100110100 //  + 127 -127 1.01100110011001100110100 //  + 0        1.01100110011001100110100 // //f=1.600000 //hex=3F CC CC CE //bin=00111111110011001100110011001110 //bin=0 01111111   10011001100110011001110 //  + 127 -127 1.10011001100110011001110 //  + 0        1.10011001100110011001110 // //f=1.800000 //hex=3F E6 66 68 //bin=00111111111001100110011001101000 //bin=0 01111111   11001100110011001101000 //  + 127 -127 1.11001100110011001101000 //  + 0        1.11001100110011001101000 // //f=2.000000 //hex=40 00 00 01 //bin=01000000000000000000000000000001 //bin=0 10000000   00000000000000000000001 //  + 128 -127 1.00000000000000000000001 //  + 1        1.00000000000000000000001 //------------ // //f=2.000000 //hex=40 00 00 00 //bin=01000000000000000000000000000000 //bin=0 10000000   00000000000000000000000 //  + 128 -127 1.00000000000000000000000 //  + 1        1.00000000000000000000000 //----------------------------------- // //d=0.000000000000000 //hex=00 00 00 00 00 00 00 00 //bin=0000000000000000000000000000000000000000000000000000000000000000 //bin=0 00000000000   0000000000000000000000000000000000000000000000000000 //  + 0     -1023 1.0000000000000000000000000000000000000000000000000000 //  + -1023       1.0000000000000000000000000000000000000000000000000000 // //d=0.200000000000000 //hex=3F C9 99 99 99 99 99 9A //bin=0011111111001001100110011001100110011001100110011001100110011010 //bin=0 01111111100   1001100110011001100110011001100110011001100110011010 //  + 1020  -1023 1.1001100110011001100110011001100110011001100110011010 //  + -3          1.1001100110011001100110011001100110011001100110011010 // //d=0.400000000000000 //hex=3F D9 99 99 99 99 99 9A //bin=0011111111011001100110011001100110011001100110011001100110011010 //bin=0 01111111101   1001100110011001100110011001100110011001100110011010 //  + 1021  -1023 1.1001100110011001100110011001100110011001100110011010 //  + -2          1.1001100110011001100110011001100110011001100110011010 // //d=0.600000000000000 //hex=3F E3 33 33 33 33 33 34 //bin=0011111111100011001100110011001100110011001100110011001100110100 //bin=0 01111111110   0011001100110011001100110011001100110011001100110100 //  + 1022  -1023 1.0011001100110011001100110011001100110011001100110100 //  + -1          1.0011001100110011001100110011001100110011001100110100 // //d=0.800000000000000 //hex=3F E9 99 99 99 99 99 9A //bin=0011111111101001100110011001100110011001100110011001100110011010 //bin=0 01111111110   1001100110011001100110011001100110011001100110011010 //  + 1022  -1023 1.1001100110011001100110011001100110011001100110011010 //  + -1          1.1001100110011001100110011001100110011001100110011010 // //d=1.000000000000000 //hex=3F F0 00 00 00 00 00 00 //bin=0011111111110000000000000000000000000000000000000000000000000000 //bin=0 01111111111   0000000000000000000000000000000000000000000000000000 //  + 1023  -1023 1.0000000000000000000000000000000000000000000000000000 //  + 0           1.0000000000000000000000000000000000000000000000000000 // //d=1.200000000000000 //hex=3F F3 33 33 33 33 33 33 //bin=0011111111110011001100110011001100110011001100110011001100110011 //bin=0 01111111111   0011001100110011001100110011001100110011001100110011 //  + 1023  -1023 1.0011001100110011001100110011001100110011001100110011 //  + 0           1.0011001100110011001100110011001100110011001100110011 // //d=1.400000000000000 //hex=3F F6 66 66 66 66 66 66 //bin=0011111111110110011001100110011001100110011001100110011001100110 //bin=0 01111111111   0110011001100110011001100110011001100110011001100110 //  + 1023  -1023 1.0110011001100110011001100110011001100110011001100110 //  + 0           1.0110011001100110011001100110011001100110011001100110 // //d=1.600000000000000 //hex=3F F9 99 99 99 99 99 99 //bin=0011111111111001100110011001100110011001100110011001100110011001 //bin=0 01111111111   1001100110011001100110011001100110011001100110011001 //  + 1023  -1023 1.1001100110011001100110011001100110011001100110011001 //  + 0           1.1001100110011001100110011001100110011001100110011001 // //d=1.800000000000000 //hex=3F FC CC CC CC CC CC CC //bin=0011111111111100110011001100110011001100110011001100110011001100 //bin=0 01111111111   1100110011001100110011001100110011001100110011001100 //  + 1023  -1023 1.1100110011001100110011001100110011001100110011001100 //  + 0           1.1100110011001100110011001100110011001100110011001100 // //d=2.000000000000000 //hex=3F FF FF FF FF FF FF FF //bin=0011111111111111111111111111111111111111111111111111111111111111 //bin=0 01111111111   1111111111111111111111111111111111111111111111111111 //  + 1023  -1023 1.1111111111111111111111111111111111111111111111111111 //  + 0           1.1111111111111111111111111111111111111111111111111111 // //d=2.200000000000000 //hex=40 01 99 99 99 99 99 99 //bin=0100000000000001100110011001100110011001100110011001100110011001 //bin=0 10000000000   0001100110011001100110011001100110011001100110011001 //  + 1024  -1023 1.0001100110011001100110011001100110011001100110011001 //  + 1           1.0001100110011001100110011001100110011001100110011001 //------------ // //d=2.000000000000000 //hex=40 00 00 00 00 00 00 00 //bin=0100000000000000000000000000000000000000000000000000000000000000 //bin=0 10000000000   0000000000000000000000000000000000000000000000000000 //  + 1024  -1023 1.0000000000000000000000000000000000000000000000000000 //  + 1           1.0000000000000000000000000000000000000000000000000000 //

user: user-6
content: 1 和0.9 之类的是否相等，不仅仅看他们是否小于 e，而且还有看你的实际环境。 你处理数据的精度和误差。

user: user-7
content: 1.0是可以准确表示, 所以直接用int就好了 *(int *)&a==*(int *)&b或者 *(int *)&a==0x3F800000