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各位CSDN的uu们你们好呀，这段时间小雅兰的内容仍然是C++string类的使用的内容，下面，让我们进入string类的世界吧！！！
string类的常用接口说明
string - C++ Reference
string类的常用接口说明
string类对象的修改操作
insert
这是在第五个位置插入xxxx这个字符串！
下面的代码的意思是头插4个x字符！
头插还可以这么写，用迭代器的方式！
#include<iostream>
#include<string>
using namespace std;
int main()
{string s1("hello world");s1.insert(5, "xxxx");cout << s1 << endl;s1.insert(0, 4, 'x');cout << s1 << endl;s1.insert(s1.begin(), 'z');cout << s1 << endl;return 0;
}insert最常见的用法还是插入字符和插入字符串！
严格来说，对于string类，insert是能少用就少用！
erase
下面两段代码的意思是：从第五个位置开始，删除四个字符
从第五个位置开始，后面有多少个字符就删多少个字符！
assign
#include<iostream>
#include<string>
using namespace std;
int main()
{string s1("hello world");s1.assign(s1);cout << s1 << endl;s1.assign(s1, 4, 7);cout << s1 << endl;s1.assign("pangrams are cool", 8);cout << s1 << endl;s1.assign("C-string");cout << s1 << endl;return 0;
} 
replace
#include<iostream>
#include<string>
using namespace std;
int main()
{string s1("hello world hello lsy");cout << s1 << endl;//所有的空格替换成%20size_t pos = s1.find(' ');while (pos != string::npos){s1.replace(pos, 1, "%20");pos = s1.find(' ');}cout << s1 << endl;return 0;
}
以前在学习C语言的时候，就写过程序实现这个功能，只是那时候还颇为复杂，学习了C++的string类之后，就简单多了，但是，这个程序写得还是不够好！
真正的问题是：每次find都要从头开始find，这样显然是没有必要的！
这样写就好多了！
int main()
{
string s1("hello world hello lsy");
cout << s1 << endl;//所有的空格替换成%20
size_t pos = s1.find(' ', 0);
while (pos != string::npos)
{
s1.replace(pos, 1, "%20");
pos = s1.find(' ', pos + 3);
}
cout << s1 << endl;
return 0;
}
但是实际上，这个程序还是不会这样写，因为replace要挪动数据，效率是很低的！
下面，小雅兰就给大家介绍一种高效率的写法：
int main()
{string s1("hello world hello lsy");cout << s1 << endl;//所有的空格替换成%20size_t pos = s1.find(' ', 0);while (pos != string::npos){s1.replace(pos, 1, "%20");//效率很低，能不用就不要用了pos = s1.find(' ', pos + 3);}cout << s1 << endl;string s2("hello world hello lsy");cout << s2 << endl;string s3;for (auto ch : s2){if (ch == ' '){s3 += "%20";}else{s3 += ch;}}cout << s3 << endl;s2.swap(s3);cout << s2 << endl;return 0;
}
swap
不过，swap是不一样的！
第一个swap会产生临时对象，会有拷贝，效率没那么高，第二个swap就是直接交换了指针！
第二种写法的唯一缺陷就是消耗了空间！
pop_back
c_str
#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<string>
using namespace std;int main()
{
string filename("test20240124.cpp");
FILE* fout = fopen(filename.c_str(), "r");
char ch = fgetc(fout);
while (ch != EOF)
{
cout << ch;
ch = fgetc(fout);
}return 0;
}
这个接口的主要目的就是兼容C！
这个程序就把小雅兰今天在文件中写的代码全部读取到控制台啦！
find+substr
要取一个文件的后缀：
int main()
{string s1("Test.cpp");string s2("Test.zip");size_t pos1 = s1.find('.');if (pos1 != string::npos){string suff = s1.substr(pos1, s1.size() - pos1);//string suff = s1.substr(pos1);cout << suff << endl;}size_t pos2 = s2.find('.');if (pos2 != string::npos){string suff = s2.substr(pos2);cout << suff << endl;}return 0;
}
但是这样写有一点小问题：
int main()
{
string s1("Test.cpp");
string s2("Test.tar.zip");size_t pos1 = s1.find('.');
if (pos1 != string::npos)
{
//string suff = s1.substr(pos1, s1.size() - pos1);
string suff = s1.substr(pos1);
cout << suff << endl;
}size_t pos2 = s2.find('.');
if (pos2 != string::npos)
{
string suff = s2.substr(pos2);
cout << suff << endl;
}
return 0;
}
取到的不是真后缀！
int main()
{string s1("Test.cpp");string s2("Test.tar.zip");size_t pos1 = s1.rfind('.');if (pos1 != string::npos){//string suff = s1.substr(pos1, s1.size() - pos1);string suff = s1.substr(pos1);cout << suff << endl;}size_t pos2 = s2.rfind('.');if (pos2 != string::npos){string suff = s2.substr(pos2);cout << suff << endl;}return 0;
}
这样才是取到的正确的后缀！
接下来，来看一个更为复杂的场景：
给定一个网址，把它的三个部分分离！
string str("https://legacy.cplusplus.com/reference/string/string/substr/");
string sub1, sub2, sub3;
pos1 = str.find(':');
sub1 = str.substr(0, pos1 - 0);
cout << sub1 << endl;pos2 = str.find('/', pos1 + 3);
sub2 = str.substr(pos1 + 3, pos2 - (pos1 + 3));
cout << sub2 << endl;sub3 = str.substr(pos2 + 1);
cout << sub3 << endl;
find_first_of
#include<iostream>
#include<string>
using namespace std;int main()
{
std::string str("Please, replace the vowels in this sentence by asterisks.");
std::size_t found = str.find_first_of("aeiou");
while (found != std::string::npos)
{
str[found] = '*';
found = str.find_first_of("aeiou", found + 1);
}std::cout << str << '\n';
return 0;
}
find_last_of
#include<iostream>
#include<string>
using namespace std;void SplitFilename(const std::string& str)
{
std::cout << "Splitting: " << str << '\n';
std::size_t found = str.find_last_of("/\\");
std::cout << " path: " << str.substr(0, found) << '\n';
std::cout << " file: " << str.substr(found + 1) << '\n';
}int main()
{
std::string str1("/usr/bin/man");
std::string str2("c:\\windows\\winhelp.exe");SplitFilename(str1);
SplitFilename(str2);return 0;
}
find_first_not_of
#include<iostream>
#include<string>
using namespace std;int main()
{
std::string str("look for non-alphabetic characters...");std::size_t found = str.find_first_not_of("abcdefghijklmnopqrstuvwxyz ");
if (found != std::string::npos)
{
std::cout << "The first non-alphabetic character is " << str[found];
std::cout << " at position " << found << '\n';
}return 0;
}
find_last_not_of
#include<iostream>
#include<string>
using namespace std;int main()
{
std::string str("Please, erase trailing white-spaces \n");
std::string whitespaces(" \t\f\v\n\r");std::size_t found = str.find_last_not_of(whitespaces);
if (found != std::string::npos)
str.erase(found + 1);
else
str.clear(); // str is all whitespacestd::cout << '[' << str << "]\n";
return 0;
}
+
int main()
{string s1(" hello ");string s2("world");string ret1 = s1 + s2;cout << ret1 << endl;string ret2 = s1 + "xx";cout << ret2 << endl;string ret3 = "xx" + s1;cout << ret3 << endl;return 0;
}
字符串最后一个单词的长度
但是这个题目有一个坑，就是：不管是scanf还是cin，默认是用空格或者换行去分割！
#include <iostream>
using namespace std;
#include<string>
int main()
{string str;getline(cin,str);size_t pos=str.rfind(' ');if(pos!=string::npos){cout<<str.size()-(pos+1)<<endl;}else {cout<<str.size()<<endl;}return 0;
}
好啦，string的使用的部分到这里就结束啦，之前的文章：
https://xiaoyalan.blog.csdn.net/article/details/135110694?spm=1001.2014.3001.5502
https://xiaoyalan.blog.csdn.net/article/details/135133181?spm=1001.2014.3001.5502
还要继续加油！！！
