一、C++标准库的主要组件：
1、标准C库
2、I/O流技术（对标准输入输出设备称为标准I/O,对在外磁盘上文件的输入输出称为文件I/O,对内存中指定的字符串存储空间的输入输出称为串I/O）
3、string类模版
4、容器(vector、list、queue、stack、deque、map、set和bitset）
5、算法
6、对国际化的支持
7、对数字处理的支持
8、诊断支持（3中报错方式：C的断言、错误号、例外）
二、I/O流技术
C++为实现数据的输入输出定义了一个庞大的类库，它包括的类主要有ios、istream、ostream、iostream、ifstream、ofstream、fstream、istrstream、ostrstream、strstream等，其中ios为根基类，其余的都是它的直接或者间接派生类。
ios直接派生四个类：输入流iostream、输出流ostream、文件流基类fstream和字符串基类strstream.
通过上面的介绍很容易理解C++中的I/O流库都包含在iostream、fstream、strstream这三个类库文件中。
C++不仅仅提供了上面的三个类库，还为用户提供了提供了标准I/O操作中的类对象，分别是cin、cout、cerr、clog
格式控制操作符：
#include <iostream> //其实iomanip中包含iostream,所以该行可省略
#include <iomanip>
using namespace std;
int main(){
int x = 30, y = 300, z = 1024;
cout << x << ‘ ‘ << y << ‘ ‘ << z << endl;
//八进制输出
cout << oct << x << ‘ ‘ << y << ‘ ‘ << z << endl;
//十六进制输出
cout << hex << x << ‘ ‘ << y << ‘ ‘ << z << endl;
//设置提示符和字母大写输出
cout << setiosflags(ios::showbase | ios::uppercase);
cout << x << ‘ ‘ << y << ‘ ‘ << z << endl;
cout << resetiosflags(ios::showbase | ios::uppercase);
cout << x << ‘ ‘ << y << ‘ ‘ << z << endl;
//按十进制输出
cout << dec << x << ‘ ‘ << y << ‘ ‘ << z << endl;
return 0;
}
自定义流操作符：
#include <iostream>
using namespace std;
ostream &lin(ostream &myos){
return myos << "\n-----------------";
}
int main(){
cout << lin << lin << lin << endl;
return 0;
}
I/O操作符重载：
#include <iostream>
#include <string.h>
using namespace std;
class Student{
friend ostream& operator << (ostream& ot, Student& popup);
char name[10];
unsigned int age;
unsigned long num;
public:
Student(char *na, unsigned int al, unsigned long number):age(al),
num(number){
strcpy(name, na);
}
};
ostream& operator << (ostream& ot, Student& popup){
ot << "Name:" << popup.name << endl << "Age:" << popup.age << endl
<< "Number:" << popup.num << endl << "---------------------" << endl;
return ot;
}
int main(){
Student a("Wang", 18, 1234), b("zhao", 19, 4312), c("liu", 20, 2341);
cout << a << b << c;
return 0;
}
写入文件：
#include <iostream>
#include <stdlib.h>
#include <fstream>
using namespace std;
int main(void){
//定义输出文件流，并打开相应的文件
ofstream f1("a:wr1.dat");
if(!f1){
cerr << "a:wr1.data file not open!" << endl;
}
for(int i=0; i<21 ; i++){
f1 << i << ‘ ‘;
}
f1.close();
return 0;
}
读文件内容：
#include <iostream>
#include <std.ib.h>
#include <fstream>
int main(){
//规定打开的文件时输入文件，若文件不存在则返回打开失败信息
ifstream f1("wrl.dat", ios::in | ios::nocreate);
//当f1打开失败时进行错误处理
if(!f1){
cerr << "wr1.data file not open!" << endl;
exit(1);
}
int x;
while(f1 >> x)
cout << x << ‘ ‘;
cout << endl;
f1.close();
return 0;
}
输入输出流操作：
#include <iostream>
#include <strstream>
using namespace std;
int main(){
char a[50];
char b[50];
istrstream sin(a); //定义一个输入字符串流sin,使用的字符数组为a
//定义一个输出字符串流sout，使用的字符数组为b
ostrstream sout(b, sizeof(b));
//从键盘上输入字符
cin.getline(a, sizeof(a));
char ch = ‘ ‘;
int x;
while(ch !=‘@‘){
//使用‘@‘字符作为字符串流结束标志
if(ch >= 48 && ch <= 57){
//将字符压入流中
sin.putback(ch);
sin >> x;
//存入输出流
sout << x << ‘ ‘;
}
//每次取出一个字符
sin.get(ch);
}
sout << ‘@‘ << ends;
//输出输出流的内容
cout << b;
cout << endl;
return 0;
}
构造字符串：
#include <string>
#include <iostream>
using namespace std;
int main(){
string Mystring1(10, ‘ ‘);
string Mystring2 = "This is a string";
string Mystring3(Mystring2);
cout << "string1 is : " << Mystring1 << endl;
cout << "string2 is : " << Mystring2 << endl;
cout << "stirng3 is : " << Mystring3 << endl;
return 0;
}
字符串判断函数：
1、empty()
2、length()
3、resize()改变长度
#include <iostream>
#include <string>
using namespace std;
int main(){
string TestString = "ll11223344565666";
cout << TestString << "\n size: " << TestString.length() << endl;
TestString.resize(5);
cout << TestString << "\n size: " << TestString.size() << endl;
TestString.resize(10);
cout << TestString << "\n size: " << TestString.size() << endl;
TestString.resize(15, ‘6‘);
cout << TestString << "\n size: " << TestString.size() << endl;
return 0;
}
4、append()
5、c_str()
#include <string>
#include <iostream>
using namespace std;
int main(){
string str1("012");
string str2("345");
cout << "str1 = " << str1.c_str() << endl;
cout << "str2 = " << str2 << endl;
//把字符串str2增加到str1尾部
str1.append(str2);
cout << "str1 = " << str1 << endl;
//返回的是一个常量指针
const char* ch = str1.c_str();
for(int i=0; i<str1.length(); i++){
cout << ch[i] << ‘ ‘;
}
cout << endl;
str1.append(str2.c_str(), 2); //把字符串中的前两个元素插入到str1尾部
str1.append(1, ‘A‘);
str1.append(str2.begin(), str2.end());
cout << "str1 = " << str1 << endl;
cout << endl;
return 0;
}
字符和字符串连接
#include <string>
#include <iostream>
using namespace std;
int main(){
string result;
string S1 = "ABC";
string S2 = "DEF";
char CP1[] = "GHI";
char C = ‘J‘;
cout << "S1 is " << S1 << endl;
cout << "S2 is " << S2 << endl;
cout << "C is " << C << endl;
result = CP1 + S1;
cout << "CP1 + S1 is " << result << endl;
result = S1 + C;
cout << "S1 + C is " << result << endl;
result = S1 + S2;
cout << "S1 + S2 is " << result << endl;
result = CP1 + C + S1;
cout << "CP1 + C + S1 is " << result << endl;
result = S1 + CP1 + C;
cout << "S1 + CP1 + C is " << result << endl;
return 0;
}
字符串迭代：
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
int main(){
const string hello("Hello, how are you?");
string s(hello.begin(), hello.end());
cout << "s : " << s << endl;
string::iterator pos;
for(pos = s.begin(); pos != s.end(); ++pos){
cout << *pos << ‘ ‘;
}
cout << endl;
//字符串翻转
reverse(s.begin(), s.end());
cout << "reverse: " << s << endl;
//去除重复元素
s.erase(unique(s.begin(), s.end()), s.end());
cout << "no duplictes: " << s << endl;
}
时间： 2024-10-16 11:02:46