一、IO流
流、一连串连续不断的数据集合。
看下图,继承关系
using namespace
流类的构造函数
eg:ifstream::ifstream (const char* szFileName, int mode = ios::in, int);
c
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ifstream inFile("c:\\tmp\\test.txt", ios::in);
if (inFile)
inFile.close();
else
cout << "test.txt doesn't exist" << endl;
ofstream oFile("test1.txt", ios::out);
if (!oFile)
cout << "error 1";
else
oFile.close();
fstream fFile("tmp\\test2.txt", ios::out | ios::in);
if (!fFile2)
cout << "error 2";
else
fFile.close();
return 0;
}
c
#include <iostream>
#include <fstream>
using namespace std;
int arr[100];
int main()
{
int num = 0;
ifstream inFile("i.txt", ios::in);//文本模式打开
if (!inFile)
return 0;//打开失败
ofstream outFile("o.txt",ios::out);
if (!outFile)
{
outFile.close();
return 0;
}
int x;
while (inFile >> x)
arr[num++] = x;
for (int i = num - 1; i >= 0; i--)
outFile << arr[i] << " ";
inFile.close();
outFile.close();
return 0;
}
ostream::write 成员函数:ostream & write(char* buffer, int count);
c
class Person
{
public:
char m_name[20];
int m_age;
};
int main()
{
Person p;
ofstream outFile("o.bin", ios::out | ios::binary);
while (cin >> p.m_name >> p.m_age)
outFile.write((char*)&p, sizeof(p));//强制类型转换
outFile.close();
//heiren 烫烫烫烫烫烫啼
return 0;
}
一个字节一个字节地读写,不如一次读写一片内存区域快。每次读写的字节数最好是 512 的整数倍
c
#include <iostream>
#include <fstream>
//#include <vector>
//#include<cstring>
using namespace std;
class Person
{
public:
char m_name[20];
int m_age;
};
int main()
{
Person p;
ifstream ioFile("p.bin", ios::in | ios::out);//用既读又写的方式打开
if (!ioFile)
return 0;
ioFile.seekg(0, ios::end); //定位读指针到文件尾部,以便用以后tellg 获取文件长度
int L = 0, R; // L是折半查找范围内第一个记录的序号
// R是折半查找范围内最后一个记录的序号
R = ioFile.tellg() / sizeof(Person) - 1;
do {
int mid = (L + R) / 2;
ioFile.seekg(mid *sizeof(Person), ios::beg);
ioFile.read((char *)&p, sizeof(p));
int tmp = strcmp(p.m_name, "Heiren");
if (tmp == 0)
{
cout << p.m_name << " " << p.m_age;
break;
}
else if (tmp > 0)
R = mid - 1;
else
L = mid + 1;
} while (L <= R);
ioFile.close();
system("pause");
return 0;
}