六、C++的I/O流库
C：fopen/fclose/fread/fwrite/fprintf/fscanf/fseek/ftell...
C++：对基本的I/O操作做了类的封装，其功能没有任何差别，用法和C的I/O流也非常近似。
七、格式化I/O
<</>>
1 /* 2 *格式化I/O练习 3 */ 4 #include <iostream> 5 #include <fstream> 6 using namespace std; 7 int main (void) { 8 ofstream ofs ("format.txt"); 9 if (! ofs) { 10 perror ("打开文件失败"); 11 return -1; 12 } 13 ofs << 1234 << ' ' << 56.78 << ' ' << "linux" 14 << '\n'; 15 ofs.close (); 16 ofs.open ("format.txt", ios::app); 17 if (! ofs) { 18 perror ("打开文件失败"); 19 return -1; 20 } 21 ofs << "append_a_line\n"; 22 ofs.close (); 23 ifstream ifs ("format.txt"); 24 if (! ifs) { 25 perror ("打开文件失败"); 26 return -1; 27 } 28 int i; 29 double d; 30 string s1, s2; 31 ifs >> i >> d >> s1 >> s2; 32 cout << i << ' ' << d << ' ' << s1 << ' ' 33 << s2 << endl; 34 ifs.close (); 35 return 0; 36 }
八、非格式化I/O
put/get
1 /* 2 *非格式化的I/O练习 3 */ 4 #include <iostream> 5 #include <fstream> 6 using namespace std; 7 int main (void) { 8 ofstream ofs ("putget.txt"); 9 if (! ofs) { 10 perror ("打开文件失败"); 11 return -1; 12 } 13 for (char c = ' '; c <= '~'; ++c) 14 if (! ofs.put (c)) { 15 perror ("写入文件失败"); 16 return -1; 17 } 18 ofs.close (); 19 ifstream ifs ("putget.txt"); 20 if (! ifs) { 21 perror ("打开文件失败"); 22 return -1; 23 } 24 char c; 25 while ((c = ifs.get ()) != EOF) 26 cout << c; 27 cout << endl; 28 if (! ifs.eof ()) { 29 perror ("读取文件失败"); 30 return -1; 31 } 32 ifs.close (); 33 return 0; 34 }
九、随机I/O
seekp/seekg
tellp/tellg
1 /* 2 * seekp/seekg练习 3 * tellp/tellg练习 4 * */ 5 #include <iostream> 6 #include <fstream> 7 using namespace std; 8 int main (void) { 9 fstream fs ("seek.txt", ios::in | ios::out); 10 if (! fs) { 11 perror ("打开文件失败"); 12 return -1; 13 } 14 fs << "0123456789"; 15 cout << fs.tellp () << endl;//tellp返回当前put操作位置 16 cout << fs.tellg () << endl;//tellg返回当前get操作位置 17 fs.seekp (-3, ios::cur); 18 fs << "XYZ"; 19 fs.seekg (4, ios::beg); 20 int i; 21 fs >> i; 22 cout << i << endl; 23 cout << fs.tellg () << endl; 24 cout << fs.tellp () << endl; 25 fs.seekg (-6, ios::end); 26 fs << "ABC"; 27 fs.close (); 28 return 0; 29 }
十、二进制I/O
read/write
1 /* 2 *read/write练习 3 */ 4 #include <iostream> 5 #include <fstream> 6 #include <cstring> 7 using namespace std; 8 class Dog { 9 public: 10 Dog (const string& name = "", int age = 0) : 11 m_age (age) { 12 strcpy (m_name, name.c_str ()); 13 } 14 void print (void) const { 15 cout << m_name << "，" << m_age << endl; 16 } 17 private: 18 char m_name[128]; 19 int m_age; 20 }; 21 int main (void) { 22 ofstream ofs ("dog.dat"); 23 Dog dog ("小白", 25); 24 ofs.write ((char*)&dog, sizeof (dog)); 25 ofs.close (); 26 ifstream ifs ("dog.dat"); 27 Dog dog2; 28 ifs.read ((char*)&dog2, sizeof (dog2)); 29 dog2.print (); 30 ifs.close (); 31 return 0; 32 }
1 /* 2 * 使用按位异或对文件加密和解密 3 * */ 4 #include <iostream> 5 #include <fstream> 6 #include <stdexcept> 7 #include <cstdlib> 8 using namespace std; 9 #define BUFSIZE (1024*10) 10 int _xor (const char* src, const char* dst, 11 unsigned char key) { 12 ifstream ifs (src, ios::binary); 13 if (! ifs) { 14 perror ("打开源文件失败"); 15 return -1; 16 } 17 ofstream ofs (dst, ios::binary); 18 if (! ofs) { 19 perror ("打开目标文件失败"); 20 return -1; 21 } 22 char* buf = NULL; 23 try { 24 buf = new char[BUFSIZE]; 25 } 26 catch (bad_alloc& ex) { 27 cout << ex.what () << endl; 28 return -1; 29 } 30 while (ifs.read (buf, BUFSIZE)) { 31 for (size_t i = 0; i < BUFSIZE; ++i) 32 buf[i] ^= key; 33 if (! ofs.write (buf, BUFSIZE)) { 34 perror ("写入文件失败"); 35 return -1; 36 } 37 } 38 if (! ifs.eof ()) { 39 perror ("读取文件失败"); 40 return -1; 41 } 42 for (size_t i = 0; i < ifs.gcount (); ++i) 43 buf[i] ^= key; 44 if (! ofs.write (buf, ifs.gcount ())) { 45 perror ("写入文件失败"); 46 return -1; 47 } 48 delete[] buf; 49 ofs.close (); 50 ifs.close (); 51 return 0; 52 } 53 int enc (const char* plain, const char* cipher) { 54 srand (time (NULL)); 55 unsigned char key = rand () % 256; 56 if (_xor (plain, cipher, key) == -1) 57 return -1; 58 cout << "密钥：" << (unsigned int)key << endl; 59 return 0; 60 } 61 int dec (const char* cipher, const char* plain, 62 unsigned char key) { 63 return _xor (cipher, plain, key); 64 } 65 int main (int argc, char* argv[]) { 66 if (argc < 3) { 67 cerr << "用法：" << argv[0] 68 << " <明文文件> <密文文件>" << endl; 69 cerr << "用法：" << argv[0] 70 << " <密文文件> <明文文件> <密钥>" 71 << endl; 72 return -1; 73 } 74 if (argc < 4) 75 return enc (argv[1], argv[2]); 76 else 77 return dec (argv[1], argv[2], 78 atoi (argv[3])); 79 return 0; 80 }
十一、格式控制
in a;
printf ("%d%x\n", a, a)
cout << a << endl;
流函数,例如cout.precision(10)
流控制符,流控制符是对象,例如setprecision(10)。使用流控制符需要include <iomanip>
cout << hex << a;
cout << setw (10) << a;
1 /* 2 *格式控制练习 3 */ 4 #include <iostream> 5 #include <iomanip> 6 #include <cmath> 7 #include <fstream> 8 #include <sstream> 9 using namespace std; 10 int main (void) { 11 cout << sqrt (2) << endl; 12 cout.precision (10); // 10位有效数字 13 cout << sqrt (2) << endl; 14 cout << sqrt (2) * 100 << endl; 15 cout << setprecision (5) << sqrt (2) << endl 16 << sqrt (2) * 100 << endl; 17 cout << "当前精度：" << cout.precision () 18 << endl; 19 cout << setprecision (2) << 1.24 << ' ' << 1.25 20 << ' ' << 1.26 << endl; 21 cout << showbase << hex << 127 << endl; 22 cout << oct << 127 << endl; 23 cout << dec << 127 << endl; 24 cout << noshowbase << hex << 127 << dec << endl; 25 cout << setw (12) << 127 << 721 << endl; 26 cout << setfill ('$') << left << setw (12) 27 << 127 << endl; 28 cout.precision (10); 29 cout.setf (ios::scientific); 30 cout << sqrt (2) << endl; 31 cout.setf (ios::fixed); 32 cout << sqrt (2) << endl; 33 cout << 12.00 << endl; 34 cout << showpoint << 12.00 << endl; 35 cout << noshowpoint << 12.00 << endl; 36 ifstream ifs ("stream.txt"); 37 ifs.unsetf (ios::skipws); 38 char c; 39 while (ifs >> c) 40 cout << c; 41 ifs.setf (ios::skipws); 42 ifs.clear (); // 复位 43 ifs.seekg (ios::beg); 44 while (ifs >> c) 45 cout << c; 46 ifs.close (); 47 cout << endl; 48 int i = 1234; 49 double d = 56.78; 50 string s = "tarena"; 51 ostringstream oss; 52 oss << i << ' ' << d << ' ' << s; 53 string str = oss.str (); 54 cout << str << endl; 55 str = "hello 3.14 pai"; 56 istringstream iss; 57 iss.str (str); 58 iss >> s >> d >> str; 59 cout << s << ' ' << d << ' ' << str << endl; 60 return 0; 61 }
