目录
一：IO流的继承关系：
二：输入输出功能
1. 基本用法
2. 格式化输入
3.非格式化输入
4. 格式化输出
三：流
1. 字符流
2. 向字符流中写入数据
3. 从字符流中读出数据
4. 清空字符流
5.完整的例子
四：文件流
一：IO流的继承关系：
| 类 | 含义 |
|---|---|
| basic_streambuf | 读取或写入数据 |
| ios_base | 独立于字符类型的流属性 |
| basic_ios | 依赖于字符类型的流属性 |
| basic_istream | 用于读取数据的流基类 |
| basic_iostream | 用于写入数据的流基类 |
| basic_iostream | 用于读写数据的流基类 |
二：输入输出功能
typedef basic_istream<char> istream;
typedef basic_ostream<char> ostream;1. 基本用法
#include <iostream>
int main(){
std::cout << "Type in your numbers";
std::cout << "(Quit with an arbitrary character): " << std::endl;
// 2000 <Enter> 11 <a>
int sum{0};
int val;
while (std::cin >> val) sum += val;
std::cout << "Sum: " << sum; // Sum: 2011
}2. 格式化输入
include <iostream>
int main()
{
int a, b;
std::cout << "Two natural numbers: " << std::endl;
std::cin >> a >> b; // < 2000 11>
std::cout << "a: " << a << " b: " << b;
}3.非格式化输入
#include <iostream>
int main()
{
std::string line;
std::cout << "Write a line: " << std::endl;
std::getline(std::cin, line); // <Only for testing purpose.>
std::cout << line << std::endl; // Only for testing purpose.
std::cout << "Write numbers, separated by;" << std::endl;
while (std::getline(std::cin, line, ';') )
{
std::cout << line << " ";
}
}4. 格式化输出
#include <iostream>
int main()
{
int num{2011};
std::cout.setf(std::ios::hex, std::ios::basefield);
std::cout << num << std::endl; // 7db
std::cout.setf(std::ios::dec, std::ios::basefield);
std::cout << num << std::endl; // 2011
std::cout << std::hex << num << std::endl; // 7db
std::cout << std::dec << num << std::endl; // 2011
}#include <iostream>
#include <fstream>
#include <iomanip>
#include <iostream>
int main()
{
std::cout.fill('#');
std::cout << -12345;
std::cout << std::setw(10) << -12345; // ####-12345
std::cout << std::setw(10) << std::left << -12345; // -12345####
std::cout << std::setw(10) << std::right << -12345; // ####-12345
std::cout << std::setw(10) << std::internal << -12345; //-####12345
std::cout << std::oct << 2011; // 3733
std::cout << std::hex << 2011; // 7db
std::cout << std::showbase;
std::cout << std::dec << 2011; // 2011
std::cout << std::oct << 2011; // 03733
std::cout << std::hex << 2011; // 0x7db
std::cout << 123.456789; // 123.457
std::cout << std::fixed;
std::cout << std::setprecision(3) << 123.456789; // 123.457
std::cout << std::setprecision(6) << 123.456789; // 123.456789
std::cout << std::setprecision(9) << 123.456789; // 123.456789000
std::cout << std::scientific;
std::cout << std::setprecision(3) << 123.456789; // 1.235e+02
std::cout << std::setprecision(6) << 123.456789; // 1.234568e+02
std::cout << std::setprecision(9) << 123.456789; // 1.234567890e+02
std::cout << std::hexfloat;
std::cout << std::setprecision(3) << 123.456789; // 0x1.edd3c07ee0b0bp+6
std::cout << std::setprecision(6) << 123.456789; // 0x1.edd3c07ee0b0bp+6
std::cout << std::setprecision(9) << 123.456789; // 0x1.edd3c07ee0b0bp+6
std::cout << std::defaultfloat;
std::cout << std::setprecision(3) << 123.456789; // 123
std::cout << std::setprecision(6) << 123.456789; // 123.457
std::cout << std::setprecision(9) << 123.456789; // 123.456789
}三：流
1. 字符流
//String stream for the input of data of type char and wchar_t.
std::istringstream and std::wistringstream
//String stream for the output of data of type char and wchar_t.
std::ostringstream and std::wostringstream
//String stream for the input or output of data of type char and wchar_t.
std::stringstream and std::wstringstream
2. 向字符流中写入数据
std::stringstream os;
os << "New String";
os.str("Another new String");3. 从字符流中读出数据
std::string os;
std::string str;
os >> str;
str= os.str();4. 清空字符流
std::stringstream os;
os.str("");5.完整的例子
#include <iostream>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <sstream>
template <typename T>
T StringTo(const std::string& source) {
std::istringstream iss(source);
T ret;
iss >> ret;
return ret;
}
template <typename T>
std::string ToString(const T& n) {
std::ostringstream tmp;
tmp << n;
return tmp.str();
}
int main()
{
std::cout << "5= " << StringTo<int>("5"); // 5
std::cout << "5 + 6= " << StringTo<int>("5") + 6; // 11
std::cout << ToString(StringTo<int>("5") + 6); // "11"
std::cout << "5e10: " << std::fixed << StringTo<double>("5e10"); // 50000000000
}四：文件流
//File stream for the input of data of type char and wchar_t.
std::ifstream and std::wifstream
//File stream for the output of data of type char and wchar_t.
std::ofstream and std::wofstream
//File stream for the input and output of data of type char and wchar_t.
std::fstream and std::wfstream
//Data buffer of type char and wchar_t.
std::filebuf and std::wfilebuf
#include <fstream>
int main()
{
std::ifstream in("inFile.txt");
std::ofstream out("outFile.txt");
out << in.rdbuf();
}#include <fstream>
#include <iostream>
#include <istream>
#include <string>
void writeFile(const std::string name) {
std::ofstream outFile(name);
if (!outFile) {
std::cerr << "Could not open file " << name << std::endl;
exit(1);
}
for (unsigned int i = 0; i < 10; ++i) {
outFile << i << " 0123456789" << std::endl;
}
}
int main()
{
std::string random{ "random.txt" };
writeFile(random);
std::ifstream inFile(random);
if (!inFile) {
std::cerr << "Could not open file " << random << std::endl;
exit(1);
}
std::string line;
std::cout << inFile.rdbuf();
// 0 0123456789
// 1 0123456789
// 9 0123456789
std::cout << inFile.tellg() << std::endl; // 200
inFile.seekg(0); // inFile.seekg(0, std::ios::beg);
std::getline(inFile, line);
std::cout << line; // 0 0123456789
inFile.seekg(20, std::ios::cur);
std::getline(inFile, line);
std::cout << line; // 2 0123456789
inFile.seekg(-20, std::ios::end);
std::getline(inFile, line);
std::cout << line; // 9 0123456789
}五：IO流运算符重载，支持用户自定义类型输入输出
friend std::istream& operator>> (std::istream& in, Fraction& frac);
friend std::ostream& operator<< (std::ostream& out, const Fraction& frac);#include <fstream>
#include <iostream>
#include <istream>
#include <string>
class Fraction {
public:
Fraction(int num = 0, int denom = 0) :numerator(num), denominator(denom) {}
friend std::istream& operator>> (std::istream& in, Fraction& frac);
friend std::ostream& operator<< (std::ostream& out, const Fraction& frac);
private:
int numerator;
int denominator;
};
std::istream& operator>> (std::istream& in, Fraction& frac) {
in >> frac.numerator;
in >> frac.denominator;
return in;
}
std::ostream& operator<< (std::ostream& out, const Fraction& frac) {
out << frac.numerator << "/" << frac.denominator;
return out;
}
int main()
{
Fraction frac(3, 4);
std::cout << frac; // 3/4
std::cout << "Enter two numbers: ";
Fraction fracDef;
std::cin >> fracDef; // <1 2>
std::cout << fracDef; // 1/2
}
