[C ++] common pitfalls numerical value of the type overflow and truncation (3)

0. Introduction

This section is "[C ++] common pitfalls numerical value of the type overflow and truncation (1)" supplement focuses on floating-point values overflow.

1. Knowledge

(1) floating-point data in the following ranges:

Single-precision	float	3.4 * 10^-38 ~ 3.4 * 10^38
Double	double	1.7 * 10^-308 ~ 1.7 * 10^308
Long double	long double	1.7 * 10^-308 ~ 1.7 * 10^308

C ++ and the absence of uniform accuracy of various types of data, scale and proportion of the number of bytes in memory, various C ++ compiler system to make arrangements according to their circumstances [1]. In VC6.0, float, double, long double accounting 4,8,8 bytes.

(2) is converted into a binary floating-point number

Float into an integer part and a fractional part, integer part according to " In addition to taking more than two reverse writing rules" will be converted to a binary floating-point written on the left of the decimal part in accordance with the " by-two rounded positive sequence written law" will be convert it to a binary floating-point written on the right side of [2]. Examples are as follows:

2. floating-point value range overflow

// ConsoleApplication1.cpp: custom console application entry point.
//
 
#include " stdafx.h " 
#include <iostream> 
#include <iostream> 
#include <the cstddef> 
#include <typeinfo>

int main () {
    system("color 3f");
    float fTest1 = 3.4e33;
    float fTest2 = 3.4e38;
    float fTest3 = 3.4e39;
    printf("fTest1:   %d:   Dec: %d;  Hex: %x;  size: %d\n", fTest1, fTest1, fTest1, sizeof(fTest1));
    printf("fTest2:   %d:   Dec: %d;  Hex: %x;  size: %d\n", fTest2, fTest2, fTest2, sizeof(fTest2));
    printf("fTest3:   %d:   Dec: %d;  Hex: %x;  size: %d\n", fTest3, fTest3, fTest3, sizeof(fTest3));
    //std::cout << fTest1 << std::endl;

    system("pause");
    return 0;
}

operation result:

Here, two questions arise:

(1) fTest2 and fTest3 appeared overflow;

(2) fTest2 与 fTest3 溢出后，并没有使用多余的位来表示，“【C++】常见易犯错误之数值类型取值溢出与截断(3)”中提到，short 型溢出使用多余位来表示；但这里显然没有出现这种情况。

(2) 尚未解决，标红

参考文献

[1] 谭浩强.C++程序设计[M].北京：清华大学出版社，P18.

[2] 浮点数转二进制与浮点数据在计算机中的表示. https://blog.csdn.net/csdn1829/article/details/79376073.

[C ++] common pitfalls numerical value of the type overflow and truncation (3)

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