3.2.2 string对象上的操作-string的empty和size操作_c++ string empty 和size-优快云博客

本文通过三个C++代码示例，展示了如何使用标准库中的string类来获取字符串大小，读取并打印超过指定长度的行，以及读取并丢弃空白行。这些示例涵盖了基本的字符串操作技巧，如测量字符串长度、读取输入和条件打印。

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书中页数：P78
代码名称：string_size.cc string_size2.cc string_size3.cc

//  string_size.cc
#include <string>
using std::string;

#include <iostream>
using std::cout; using std::endl;

string st1;       // empty string
string st2(st1);  // st2 is a copy of st1

int main()
{
    string st("The expense of spirit\n");
    cout << "The size of " << st << "is " << st.size()
         << " characters, including the newline" << endl;
    return 0;
}

//string_size2.cc
#include <cstddef>
using std::size_t;

#include <string> 
using std::string; using std::getline;

#include <iostream> 
using std::cin; using std::cout; using std::endl;

int main() 
{
	string line;

	// read input a line at a time and print lines that are longer than 80 characters
	while (getline(cin, line))
		if (line.size() > 80)
			cout << line << endl;

	return 0;
}

//string_size3.cc
#include <string> 
using std::string; using std::getline;

#include <iostream> 
using std::cin; using std::cout; using std::endl;

int main() 
{
	string line;

	// read input a line at a time and discard blank lines
	while (getline(cin, line))
		if (!line.empty())
			cout << line << endl;

	return 0;
}