C++心决之stl中那些你不知道的秘密(string篇)

3.5 string类的模拟实现

//string.h
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;
namespace mystr {
class string
{
public:
//迭代器, 因为字符串底层内存连续, 所以可以简单的定义成指针
typedef char* iterator;
typedef const char* const_iterator;
//配合范围for循环
iterator begin() { return _str; }
iterator end() { return _str + _size; }
//兼容常量字符串
const_iterator begin() const { return _str; }
const_iterator end() const { return _str + _size; }
//string();
string(const char* str = "");
string(const string& s);
string& operator=(string temp) { swap(temp); return *this; }
~string() { delete[] _str; _str = nullptr; _size = _capacity = 0; }
//返回C语言字符数组
const char* c_str() const { return _str; }

size_t size() const { return _size; }
char& operator[](size_t pos) { assert(pos < _size); return _str[pos]; }
const char& operator[](size_t pos) const{ assert(pos < _size); return _str[pos]; }
//重置大小
void reserve(size_t n);

void push_back(char ch) { insert(_size, ch); }
void append(const char* str) { insert(_size, str); }

string& operator+=(char ch) { insert(_size, ch); return *this; }
string& operator+=(const char* str) { insert(_size, str); return *this; };

void insert(size_t pos, char ch);
void insert(size_t pos, const char* str);
void erase(size_t pos = 0, size_t len = npos);

size_t find(char ch, size_t pos = 0) {
for (size_t i = pos; i < _size; i++) if (_str[i] == ch) return i;
return npos;
}
size_t find(const char* str, size_t pos = 0) { return strstr(_str + pos, str) - _str; }

void swap(string& s);
string substr(size_t pos = 0, size_t len = npos);

bool operator<(const string& s) const { return strcmp(_str, s._str) < 0; }
bool operator>(const string& s) const { return !(*this <= s); }
bool operator<=(const string& s) const { return !(*this > s); }
bool operator>=(const string& s) const { return !(*this < s); }
bool operator==(const string& s) const {return strcmp(_str, s._str) == 0; }
bool operator!=(const string& s) const { return !(*this == s); }
void clear() { _str[0] = '\0'; _size = 0; }


private:
char* _str;
size_t _size;
size_t _capacity;
//一般static变量的定义要放在类外, 整型是特例
const static size_t npos = -1;
};
void swap(string& s1, string& s2);
istream& operator>>(istream& ci, string& s);
ostream& operator<<(ostream& co, string& s);
}

//string.cpp
#include "string.h"
namespace mystr {
string::string(const char* str):_size(strlen(str)) {
_str = new char[_size + 1];
_capacity = _size;
strcpy(_str, str);
}
string::string(const string& s) {
string temp(s._str);
swap(temp);
}
void string::reserve(size_t n) {
if (_capacity < n) {
char* temp = new char[n + 1];
strcpy(temp, _str);
delete[] _str;
_str = temp;
_capacity = n;
}
}
void string::insert(size_t pos, char ch) {
assert(pos <= _size);
if (_size == _capacity) {
size_t newcapacity = _capacity == 0 ? 4 : 2 * _capacity;
reserve(newcapacity);
}
size_t end = _size + 1;
while (end > pos) _str[end] = _str[end - 1], --end;
_str[pos] = ch;
_size++;
}
void string::insert(size_t pos, const char* str) {
assert(pos <= _size);
size_t len = strlen(str);
if (_size + len > _capacity) reserve(_size + len);
size_t end = _size + len;
while (end > pos + len - 1) _str[end] = _str[end - len], --end;
memcpy(_str + pos, str, len);
_size += len;
}
void string::erase(size_t pos, size_t len) {
if (len > _size - pos) _str[pos] = '\0', _size = pos;
else strcpy(_str + pos, _str + pos + len), _size -= len;
}
void string::swap(string& s) {
char* temp = _str;
_str = s._str;
s._str = temp;
std::swap(_size, s._size);
}
string string::substr(size_t pos, size_t len) {
if (len > _size - pos) { string sub(_str + pos); return sub; }
else {
string sub;
sub.reserve(len);
for (size_t i = pos; i < pos + len; i++) sub += _str[i];
return sub;
}
}
void swap(string& s1, string& s2){ s1.swap(s2); }
istream& operator>>(istream& ci, string& s) {
s.clear();
char ch = ci.get();
while (ch != ' ' && ch != '\n') s += ch, ch = ci.get();
return ci;
}
ostream& operator<<(ostream& co, string& s) {
for (size_t i = 0; i < s.size(); i++) co << s[i];
return co;
}
}

//test.cpp
#include "string.h"
namespace mystr {
void test1() {
string s1 = "1111";
string s2 = s1;
cout << s1.c_str() << endl << s2.c_str() << endl;
cout << s1.size() << endl;
}
void test2() {
string s1 = "111";
string s2 = "222222";
s1 = s2;
cout << s1.c_str() << endl;
}
void test3() {
string s1 = "111222333";
for (auto& i : s1) i += 3;
cout << s1.c_str() << endl;
const string s2 = "111222333";
for (auto& i : s2) cout << i;
cout << endl;
for (size_t i = 0; i < s1.size(); i++) cout << (s1[i] += 2);
cout << endl;
}
void test4() {
string s1 = "sadfsf";
s1.insert(2, '-');
cout << s1.c_str() << endl;
s1.insert(0, '-');
cout << s1.c_str() << endl;
s1.insert(2, "11111");
cout << s1.c_str() << endl;
s1.insert(0, "222222");
cout << s1.c_str() << endl;
}
void test5() {
string s1 = "asgfidsgf";
s1.push_back('-');
cout << s1.c_str() << endl;
s1.append("=====");
cout << s1.c_str() << endl;
s1 += 'w';
cout << s1.c_str() << endl;
s1 += "0000";
cout << s1.c_str() << endl;
s1.erase(10);
cout << s1.c_str() << endl;
s1.erase(7, 100);
cout << s1.c_str() << endl;
s1.erase(3, 2);
cout << s1.c_str() << endl;
s1.erase(0);
cout << s1.c_str() << endl;
}
void test6() {
string s1 = "ksjfghks";
cout << s1.find('h', 2) << endl;
cout << s1.find("ghk", 2) << endl;
cout << s1.find("ghksgs", 2) << endl;
}
void test7(){
string s1 = "sggsdsdf";
string s2 = "sdgfrgdb";
cout << s1.c_str() << endl;
cout << s2.c_str() << endl;
swap(s1, s2);
cout << s1.c_str() << endl;
cout << s2.c_str() << endl;
s1.swap(s2);
cout << s1.c_str() << endl;
cout << s2.c_str() << endl;
string s3 = s1.substr(2, 5);
cout << s3.c_str() << endl;
}
void test8() {
string s1, s2;
cin >> s1 >> s2;
cout << s1 << endl << s2 << endl;
}
}
int main() {
mystr::test8();
return 0;
}