0 或 1 以外的整数的布尔值是多少? [英] What is the boolean value of integers other than 0 or 1?

问题描述

我正在编写一个简单的函数来根据一组应命名为 cam1_0.bmp、cam1_1.bmp 的文件派生一个新文件名，并尝试了这个.

I was writing a simple function to derive a new filename based on a set of files that should be named as cam1_0.bmp, cam1_1.bmp, and tried this out.

static int suffix = 0;
std::string fPre("cam");
std::ifstream fs;
std::string fName;
do {
    fName = fPre;
    fName.append(std::to_string(camera)).append("_").append(std::to_string(suffix)).append(".bmp");
    fs.open(fName);
} while (fs.good() && ++suffix);

这行得通，它让我想知道对于 0 或 1 以外的数值，对应的布尔值的标准定义行为是什么.通过这个实验，我知道所有值(包括 0 以外的负值)都评估为真.按照标准，只有0被认为是假的吗?

This works and it made me wonder what is the standard, defined behavior of corresponding boolean values for number values other than 0 or 1. With this experiment I know all values including negative values other than 0 evaluates to true. Is only 0 considered to be false as per the standard?

推荐答案

在 C++ 中，整数没有布尔值.(不同的语言有不同的规则，但这个问题是关于C++的.)

In C++, integers don't have boolean values. (Different languages have different rules, but this question is about C++.)

将整数值转换 到bool 类型(通常是隐式进行的转换)的结果是明确定义的.0 转换为 bool 的结果是 false;将任何非零值转换为 bool 的结果是 true.

The result of converting an integer value to type bool (a conversion which is often done implicitly) is well defined. The result of converting 0 to bool is false; the result of converting any non-zero value to bool is true.

同样适用于浮点值(0.0 转换为 false，所有其他值转换为 true)和指针(a空指针转换为false，所有非空指针值转换为true).

The same applies to floating-point values (0.0 converts to false, all other values convert to true) and to pointers (a null pointer converts to false, all non-null pointer values convert to true).

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