string 高频使用部分

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String

头文件：include <string>
使用空间：using namesapce std;

---

创建字符串

1. 复制拷贝

//直接全部复制
string str("01234");
//从下标0开始复制3偏移量
string str("012345",3);
//从下标1开始复制3偏移量
string str("012345",1,3);

2. 用字符构造

//用3个字符a构造
string str(3,'a');

3. “=”直接复制拷贝

string str = "str";

访问元素方式，存取和修改

[],at

// [],at() :元素存取  
string stringAt = "trianglestring";  
cout << "stringAt[3] = " <<stringAt[3] << endl;  
cout << "stringAt.at(3) = " << stringAt.at(3) << endl;  

stringAt[3] = '6';  
stringAt.at(5) = '9';  
cout << "stringAt = " << stringAt << endl;

添加或者拼接字符/字符串

+ 、 append

string stringOrigin = "chen";  
string stringAppend = "yufeng";  
stringOrigin = stringOrigin + stringAppend;  
cout << "stringOrigin = " << stringOrigin << endl;  

stringOrigin.append("_OK");  
cout << "stringOriginAppend = " << stringOrigin << endl;

在指定位置插入字符串

insert

// insert：在指定position插入字符串  
string stringInsertOrigin = "trianglestring";  
stringInsertOrigin.insert(3, "__");  
cout << "stringInsertOrigin = " << stringInsertOrigin << endl;

替换字符串

replacea

// replace: 替换字符串,某个pos位置开始的size个字符替换成后面的“”字符串  
string stringReplaceOrigin = "trianglestring";  
stringReplaceOrigin.replace(3, 2, "66");  
cout << "stringReplaceOrigin = " << stringReplaceOrigin << endl;

取子字符串

substr

// substr  
  string stringSubstr = "trianglestring";  
  // 从索引为4开始的3个字符  
  cout << "stringSubstr.substr(4,3) = " << stringSubstr.substr(4,3) << endl;  
  
  // 从索引为4开始的所有字符  
  cout << "stringSubstr.substr(4) = " <<stringSubstr.substr(4) << endl;  
  
  // 整个字符  
  cout << "stringSubstr.substr() = " <<stringSubstr.substr() << endl;

查找字符/字符串

find,find_first_of,find_last_of

// find  
string stringFind = "trianglestring";  
stringFind.find('n');  
cout << "stringFind.find('n') = " << stringFind.find('n') << endl;  

cout << "stringFind.find_first_of('e') = " << stringFind.find_first_of('e') << endl;  
  
cout << "stringFind.find_last_of('e') = " << stringFind.find_last_of('e') << endl;

交换两个字符串

swap

string str1 = "chen";  
string str2 = "yufeng";  
swap(str1, str2);

比较字符串：从开始的第一个字符比较，长度是次要的

== 、!= 、 >　、<
compare

// ==，<,>,<=,>=:比较字符串  
string stringLeft = "zhen";  
string stringRight = "yufeng";  
if (stringLeft == stringRight)  
{  
  cout << "equal" << endl;  
}  

if (stringLeft != stringRight)  
{  
  cout << "not equal" << endl;  
}  

if (stringLeft < stringRight)  
{  
  cout << "stringLeft < stringRight" << endl;  
}  

if (stringLeft > stringRight)  
{  
  cout << "stringLeft > stringRight" << endl;  
}

// compare()  
string stringCompare = "trianglestring";  
int aaa = stringCompare.compare("chen"); // > 0  
int bbb = stringCompare.compare("trianglestring"); // == 0  
int ccc = stringCompare.compare("done"); // < 0  
cout << "aaa = " << aaa << ";bbb = " << bbb << ";ccc = " << ccc << endl;

删除字符串或清空字符串

erase 指定删除起始到偏移的字符
clear 清空字符串

// erase: 删除字符
string stringEraseOrigin = "trianglestring";
stringEraseOrigin.erase(2,1);
cout << "stringEraseOrigin = " << stringEraseOrigin << endl;

// clear ：删除全部字符
string stringClearOrigin = "trianglestring";
stringClearOrigin.clear();
cout << "stringClearOrigin = " << stringClearOrigin << endl;

字符串长度

size,length 没有区别
empty 判空

// size(), length():计算字符串长度  
string stringCount = "trianglestring";  
cout << "stringSize = " << stringCount.size() << endl;  
cout << "stringLength = " << stringCount.length() << endl;

// empty():判断字符串是否为空  
string stringIsEmpty = "";  
string stringNotEmpty = "chen";  
if (stringIsEmpty.empty())  
{  
    cout << "stringIsEmpty == empty" << endl;  
}  
else  
{  
    cout << "stringIsEmpty != empty" << endl;  
}  

if (stringNotEmpty.empty())  
{  
    cout << "stringNotEmpty == empty" << endl;  
}  
else  
{  
    cout << "stringNotEmpty != empty" << endl;  
}

最大容量

max_size

// max_size: 最大能表示的字符串长度 
string stringMaxSize;  
cout << "stringMaxSize = " << stringMaxSize.max_size() << endl;