C++学习第十一天

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提示：以下是本篇文章正文内容，下面案例可供参考。

一、capacity

#include<iostream>
using namespace std;

int main()
{
	string s;
	size_t old = s.capacity();
	cout << "初始：" << s.capacity() << endl;

	for (size_t i = 0; i < 100; i++)
	{
		s.push_back('x');

		if (s.capacity() != old)
		{
			cout << "扩容：" << s.capacity() << endl;
			old = s.capacity();
		}
	}

	return 0;
}

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二、reserve

#include<iostream>
using namespace std;

int main()
{
	string s;
	s.reserve(100);

	size_t old = s.capacity();
	cout << "初始：" << s.capacity() << endl;

	for (size_t i = 0; i < 100; i++)
	{
		s.push_back('x');

		if (s.capacity() != old)
		{
			cout << "扩容：" << s.capacity() << endl;
			old = s.capacity();
		}
	}

	return 0;
}

reserve价值：确定大概知道要多少空间，提前开好，减少扩容，提高效率。

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三、resize

#include<iostream>
using namespace std;

int main()
{
	string s = "hello world";
	cout << "s.size()：" << s.size() << endl;

	s.resize(13);
	cout << "s.size()：" << s.size() << endl;
	cout << "s为：" << s << endl;

	s.resize(18, 'x');
	cout << "s.size()：" << s.size() << endl;
	cout << "s为：" << s << endl;

	s.resize(8);
	cout << "s.size()：" << s.size() << endl;
	cout << "s为：" << s << endl;

	return 0;
}

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四、push_back  、append  、+=  、+

#include<iostream>
using namespace std;

int main()
{
	string ss = "hell";

	string s;
	s.push_back('o');
	cout << s << endl;

	s.append("ofjdj");
	cout << s << endl;

	s.append(ss);
	cout  << s << endl;

	s += "---";
	cout << s << endl;

	s += ss;
	cout << s << endl;

	string ret1 = ss + "hello";
	cout << ret1 << endl;

	return 0;
}

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五、insert 、erase 、repalce

#include<iostream>
using namespace std;

int main()
{
	std::string s("hello world");
	s.insert(0, 1, 'x');
	cout << s << endl;

	s.insert(s.begin(), 1, 'x');
	cout << s << endl;

	s.erase(4);
	cout << s << endl;

	std::string d("hello world");
	d.replace(5, 1, "2025");
	cout << d << endl;

	return 0;
}

  insert/erase/repalce能不用就尽量不用，因为他们都涉及挪动数据，效率不高。以及接口设计复杂繁多，需要时查一下文档即可。

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六、find 、substr

#include<iostream>
using namespace std;

int main()
{
	//文件取后缀
	string s1 = "test.cpp";
	size_t i = s1.find('.');

	string s2 = s1.substr(i);
	cout << s2 << endl;

	string s3 = "test.cpp.tar.zip";
	size_t j = s1.rfind('.');

	string s4 = s3.substr(j);
	cout << s4 << endl;

	// 找协议、域名、资源名
	string s5("https://legacy.cplusplus.com/reference/string/string/rfind/");

	string sub1, sub2, sub3;
	size_t i1 = s5.find(':');
	if (i1 != string::npos)
		sub1 = s5.substr(0,i1);
	else
		cout << "没有找到i1" << endl;
	cout << "协议名：" << sub1 << endl;

	size_t i2 = s5.find('/',i1+3);
	if (i2 != string::npos)
		sub2 = s5.substr(i1 + 3, i2 - (i1 + 3));
	else
		cout << "没有找到i2" << endl;
	cout << "域名：" << sub2 << endl;

	sub3 = s5.substr(i2 + 1);
	cout << "资源名：" << sub3 << endl;

	return 0;
}

总结

       以上就是今天要讲的内容，本文仅仅简单介绍了c++的基础知识。