C : how is double number (e.克。 123.45) 存储在 float 变量或 double 变量或 long double 变量中？

Question

#include <stdio.h>

int main () {
float a = 123.0; 

unsigned char ch, *cp;
ch = 0xff;

cp = (unsigned char *) &a;
printf ("%02x", ch&(*(cp+3)));
printf ("%02x", ch&(*(cp+2)));
printf ("%02x", ch&(*(cp+1)));
printf ("%02x\n", ch&(*(cp+0)));

/*I have written this program to see binary representation, but I can not understand the output, the binary representation?
}

Answer 1

参见维基百科:http://en.wikipedia.org/wiki/Single_precision_floating-point_format ，它将单精度浮点(典型的 C float，但取决于编译器)描述为 1 位符号、8 位偏置指数和 24 位尾数(存储 23 位) .

以你的例子为例:

123.0 = 42f60000_hex = 0 10000101 11101100000000000000000_bin
1-bit sign = 0 (indicating positive number)
8-bit biased exponent = 10000101_bin = 133_dec - 127_dec = 6_dec
23-bit mantissa = 11101100000000000000000_bin = 1.111011_bin (note implied leading 1)

Converting 1.111011_bin x 2⁶_dec = 1111011.0_bin = 123.0_dec