C++ 检测空白字符、\t、\n 等
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detecting white space characters, \t, \n, etc
提问by Matt
I am working through c++ primer 5th edition. the exercise in chapter 5 states the follow:
我正在学习 C++ 入门第 5 版。第 5 章的练习说明如下：
Exercise 5.11: Write a program that counts the number of blank spaces, tabs, and newlines read.
练习 5.11：编写一个程序，计算读取的空格、制表符和换行符的数量。
I attempted to do as exercise 5.11 did with the below code. However the code fails. Can anyone provide some examples of how i would correct the code so that when the input is read that the counter unsigned int cnt = 0;will be iterated correctly?
我试图用下面的代码做练习 5.11。但是代码失败了。谁能提供一些我将如何更正代码的示例，以便在读取输入时unsigned int cnt = 0;正确迭代计数器？
#include "stdafx.h"
#include <iostream>
int main(){
unsigned int cnt = 0;
char c1;
while (std::cin >> c1)
if (c1 == '\t' || c1 == '\n' || c1 == ' ')
++cnt;
std::cout << "The number of spaces,tabs, newlines are: " << cnt << std::endl;
system("pause");
return 0;
}
回答by Dietmar Kühl
The way to classify characters in C++ are the functions from <cctype>or the functions from <locale>: there are std::isspace()functions in both of these. Note, that you can only pass positive intvalues to the functions from <cctype>, i.e., to determine if a char cis a space you'd use:
C++中对字符进行分类的方式是函数 from<cctype>或函数 from <locale>：这std::isspace()两者都有函数。请注意，您只能将正值传递int给函数 from <cctype>，即，以确定 achar c是否是您要使用的空格：
if (std::isspace(static_cast<unsigned char>(c))) {
// c is a space
}
Just using std::isspace(c)result in undefined behavior if charis signed and cis a negative value. On typical systems non-ASCII characters (or multiple bytes of a UTF-8 encoding) use negative values.
std::isspace(c)如果char已签名且c为负值，则仅使用结果会导致未定义的行为。在典型系统上，非 ASCII 字符（或 UTF-8 编码的多个字节）使用负值。
The problems in your original code are:
您原始代码中的问题是：
'/n'is not a valid character literal; you probably meant to use'\n'.- You omitted a number of space characters, e.g.,
'\r'(carriage return) and'\v'(vertical space) - By default the formatted input operators skip all leading whitespace. To avoid this you can use
std::cin >> std::noskipws;. Personally, I would usestd::istreambuf_iterator<char>to get the characters. I guess, this is your primary problem.
'/n'不是有效的字符文字；您可能打算使用'\n'.- 您省略了一些空格字符，例如，
'\r'（回车）和'\v'（垂直空格） - 默认情况下，格式化输入运算符会跳过所有前导空格。为避免这种情况，您可以使用
std::cin >> std::noskipws;. 就个人而言，我会std::istreambuf_iterator<char>用来获取字符。我想，这是你的首要问题。
The pragmatic approach to count spaces is probably something like this:
计算空格的实用方法可能是这样的：
unsigned long spaces = std::count_if(std::istreambuf_iterator<char>(std:cin),
std::istreambuf_iterator<char>(),
[](unsigned char c){ return std::isspace(c); });
