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C语言知识

String常用接口解读

String类

string是代表了一串字符串的序列
标准string类通过类似于标准字节容器的接口为此类对象提供支持，但添加了专门设计用于处理单字节字符字符串的功能
字符串类是一个实例使用 char（即字节）作为其字符类型的basic_string类模板，其默认char_traits和分配器类型
此类处理字节与所使用的编码无关：如果用于处理多字节或可变长度字符（如 UTF-8）的序列，则此类的所有成员（如长度或大小）及其迭代器仍将根据字节（而不是实际编码字符）进行操作

成员函数

(Constructor)：构造函数
string()：构造一个空的字符串，长度为0
string(const char* str)：拷贝构造一个字符串，参数由函数传递进来
string(const char* str,size_t pos,size_t len = npos)：拷贝一个字符串的字串，从pos位置开始拷贝len个，如果len过长那么就从pos位置拷贝全部字符串
string(const char* s)：复制以\0结尾的C字符串
string(const char* s,size_t n)：拷贝字符串中的前n个字符
string(size_t n,char c)：用n个连续的c填充string
更多请参考string构造函数

案例

// string constructor
#include <iostream>
#include <string>int main ()
{std::string s0 ("Initial string");// constructors used in the same order as described above:std::string s1;std::string s2 (s0);std::string s3 (s0, 8, 3);std::string s4 ("A character sequence");std::string s5 ("Another character sequence", 12);std::string s6a (10, 'x');std::string s6b (10, 42);      // 42 is the ASCII code for '*'std::string s7 (s0.begin(), s0.begin()+7);std::cout << "s1: " << s1 << "\ns2: " << s2 << "\ns3: " << s3;std::cout << "\ns4: " << s4 << "\ns5: " << s5 << "\ns6a: " << s6a;std::cout << "\ns6b: " << s6b << "\ns7: " << s7 << '\n';return 0;
}

迭代器

begin：返回迭代器到开始位置
end：返回迭代器到结束位置
rbegin：将迭代器指向字符串的末尾
rend：将迭代器指向字符串的开头
cbegin：返回const迭代器到开始位置
cend：返回const迭代器到结束位置
crbegin：将迭代器指向字符串的末尾
crend：将const迭代器指向字符串的开头
更多内容请访问迭代器

容量

size：返回字符串的长度
length：返回字符串的长度
max_size：返回字符串的最大尺寸
capacity：返回字符串的容量
resize：重新为字符串分配大小
reserve：为字符串预留一定空间
clear：清除字符串内容
更多请访问字符串

元素访问

operator[]：获取字符串的字符
更多请访问元素访问

修改操作

operator+=：在字符串末尾添加字符或字符串
append：在字符串末尾添加字符或字符串
push_back：在字符串末尾添加字符
insert：在字符串中插入字符或字符串
erase：在字符串中清除字符或字符串
swap：交换字符串的值
更多请访问修改操作

string操作

c_str：等效的C字符串
find：找到字符串中的内容
find_first_of：找到字符串中的字符
substr：找到字符串中的子串

非成员函数重载

operator+：连接字符串
relational operator：字符串的比较
swap：交换两个字符串的内容
operator>>：流插入，用于输入
operator<<：流提取，用于输出
getline：将流中的行转换为字符串

String常用接口的模拟实现

#pragma once#include <iostream>
#include <string>
#include <assert.h>
using namespace std;namespace anmory
{class string{friend ostream& operator<<(ostream& out, const string& s);//friend istream& operator>>(istream& in, const string& s);public:const size_t npos = -1;// iterator的定义和实现typedef char* iterator;typedef const char* const_iterator;iterator begin(){return _str;}iterator end(){return _str + _size;}const_iterator begin() const{return _str;}const_iterator end() const{return _str + _size;}//你现在是在string这个类中，我重载的operator++也是stirng的，而不是迭代器的void clear(){_str[0] = '\0';_size = 0;}string(const char* str = "")// 这里不希望能够修改str的值，因此需要使用const{_size = strlen(str);_capacity = _size;_str = new char[_capacity + 1];// 预留\0的位置strcpy(_str, str);}// 构造函数string(const string& s){// 防止自我赋值导致错误if (this != &s){// 行赋值操作_size = s._size;_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, s._str);}}// 析构函数~string(){delete[] _str;_size = 0;_capacity = 0;}const char* c_str() const{return _str;}size_t size(){return _size;}size_t capacity(){return _capacity;}void swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}// 重载=，+=string& operator=(const string& s);string& operator=(string s);string& operator+=(const char* str);string& operator+=(char ch);void push_back(char ch);void append(const char* str);void reserve(size_t n);size_t resize(size_t n);size_t resize(size_t n, char c);void insert(size_t pos, char c);void insert(size_t pos, const char* str);void erase(size_t pos, size_t len);size_t find(char ch, size_t pos);size_t find(const char* str, size_t pos,size_t len);private:char* _str = 0;size_t _size = 0;size_t _capacity = 0;};bool operator>(const string& s1, const string& s2);bool operator>=(const string& s1, const string& s2);bool operator<(const string& s1, const string& s2);bool operator<=(const string& s1, const string& s2);bool operator==(const string& s1, const string& s2);bool operator!=(const string& s1, const string& s2);
}
#define _CRT_SECURE_NO_WARNINGS 1#include "string.h"namespace anmory
{const size_t npos = -1;/*istream& operator>>(istream& in, string& s){char ch;in >> ch;while (ch != ' ' && ch != '\n'){s += ch;in >> ch;}return in;}*/string& string::operator=(const string& s){{// 防止自我赋值if (this != &s){delete[] _str;// 先删去原有的字符串内容// 再进行赋值操作_size = strlen(s._str);_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, s._str);}return *this;}}string& string::operator=(string s){swap(s);return *this;}string& string::operator+=(char ch){push_back(ch);return *this;}string& string::operator+=(const char* str){append(str);return *this;}ostream& operator<<(ostream& out,const string& s){//for (size_t i = 0; i < s._size; i++)//{//	out << s._str[s._size];//}for (auto ch : s){out << ch;}//for (string::iterator iter = s.begin(); iter != s.end(); ++iter)//{//	out << *iter;//}return out;}void string::reserve(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}void string::push_back(char ch){if (_size == _capacity){reserve(_capacity == 0 ? 4 : _capacity * 2);}_str[_size] = ch;_size++;_str[_size] = '\0';// 为字符串最后手动加上\0}void string::append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){size_t newcapacity = _size + len > _capacity * 2 ? _size + len : _capacity * 2;char* tmp = new char[newcapacity + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = newcapacity;}strcat(_str, str);_size += len;}size_t string::resize(size_t n){if (n > _capacity){size_t newcapacity = n > _capacity * 2 ? n : _capacity * 2;_size = n;char* tmp = new char[_capacity + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = newcapacity;}if (n <= _size){_size = n;}return _size;}bool operator>(const string& s1, const string& s2){return strcmp(s1.c_str(), s2.c_str())>0;}bool operator>=(const string& s1, const string& s2){return s1 == s2 || s1 > s2;}bool operator<(const string& s1, const string& s2){return !(s1 >= s2);}bool operator<=(const string& s1, const string& s2){return !(s1 > s2);}bool operator==(const string& s1, const string& s2){return strcmp(s1.c_str(), s2.c_str()) == 0;}bool operator!=(const string& s1, const string& s2){return !(s1 == s2);}size_t string::resize(size_t n, char c){if (n <= _size){_size = n;_str[_size] = '\0';}if(n>_capacity){size_t newcapacity = n > _capacity * 2 ? n : _capacity * 2;char* tmp = new char[newcapacity + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = newcapacity;}if (n > _size){for (size_t i = _size; i < n; i++){_str[i] = c;}_str[_size] = '\0';_size = n;}return _size;}void string::insert(size_t pos, char c){assert(pos < _size);if (_size == _capacity){reserve(_capacity == 0 ? 4 : _capacity * 2);}size_t end = _size + 1;while (end>=pos){_str[end+1] = _str[end];end--;}_str[pos] = c;_size++;_str[_size + 1] = '\0';}void string::insert(size_t pos, const char* str){assert(pos < _size);size_t len = strlen(str);if (_size == _capacity){reserve(_capacity == 0 ? 4 : _capacity * 2);}size_t end = _size + 1;size_t end2 = end + len;while (end >= pos){_str[end + len] = _str[end];end--;}_size += len;for (size_t i = 0; i < len; i++){_str[pos + i] = str[i];}}void string::erase(size_t pos, size_t len){assert(pos < _size);size_t end = pos + len;while (_str[end] != '\0'){_str[pos++] = _str[end++];}_size -= len;_str[_size] = '\0';}size_t string::find(char ch, size_t pos){while (_str[pos] != '\0'){if (_str[pos] == ch){return ch;}}return string::npos;}size_t string::find(const char* str, size_t pos,size_t len){char* ptr = strstr(_str+pos, str);if (ptr == nullptr){return npos;}return ptr - _str;}
}
#define _CRT_SECURE_NO_WARNINGS 1#include "string.h"void test_c_str()
{anmory::string s("hello world");cout << "test_c_str:> " << s.c_str() << endl;
}void test_operator()
{anmory::string s("hello world");char ch = '*';s += ch;cout << "test+= :> " << s << endl;string tmp;//tmp = s;cout << "test= :> " << tmp << endl;
}void test_push_back()
{anmory::string s("hello world");s.push_back('x');cout << "test_push_back:> " << s << endl;
}void test_append()
{anmory::string s1("hello world");s1.append("xxxxx");cout << "test_append:> " << s1 << endl;
}void test_clear()
{anmory::string s1("hello world");s1.clear();cout << "test_clear:> " << s1 << endl;
}void test_reserve()
{anmory::string s("hello world");s.reserve(100);cout << "test_reserve:> " << s.size() << " " << s.capacity() << endl;
}void test_resize()
{anmory::string s("hello world");s.resize(19,'c');cout << "test_resize:> " << s << endl;
}void test_size()
{anmory::string s("hello");cout << "test_size:> " << s.size() << endl;
}void test_insert()
{anmory::string s("helloworld");s.insert(4, 'x');cout << "test_insert:> " << s << endl;anmory::string s1("hello world");s1.insert(5, "xxx");cout << "test_insert:> " << s1 << endl;
}void test_erase()
{anmory::string s("hello world");s.erase(5, 3);cout << "test_erase:> " << s << endl;
}int main()
{test_c_str();test_operator();test_push_back();test_append();test_clear();test_reserve();test_resize();test_size();test_insert();test_erase();return 0;
}

模拟实现中的深拷贝和浅拷贝的问题

#define _CRT_SECURE_NO_WARNINGS 1#include <iostream>
#include <vector>
#include <string>
using namespace std;class string
{
public:void swap(string s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}string(const char* str = ""){_size = strlen(str);_capacity = _size;}string(const string& s){string tmp(s);swap(tmp);}/*string& operator=(const string& s){string tmp(s);swap(tmp);return *this;}*/string& operator=(string tmp){swap(tmp);return *this;}~string(){delete[] _str;_size = 0;}
private:char* _str = nullptr;size_t _size = 0;size_t _capacity = 0;
};int main()
{/*vector<int> v1;vector<int> v2(10, 1);vector<int>::iterator it = v2.begin();while (it != v2.end()){cout << *it << " ";it++;}cout << endl;*/return 0;
}

结语

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