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cplusplus:file_processing_examples

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cplusplus:file_processing_examples [2017/02/08 20:46] – [Filenames must be c_str in pre-C++11] mithatcplusplus:file_processing_examples [2019/02/11 19:15] – [Using filenames] mithat
Line 60: Line 60:
 </file> </file>
  
-==== Filenames must be c_str in pre-C++11 ====+==== Using filenames ====
  
 <file c++ simple-file-write3.cpp>// This program writes data to a file. <file c++ simple-file-write3.cpp>// This program writes data to a file.
Line 79: Line 79:
     cin >> filename;     cin >> filename;
  
-    outfile.open(filename.cstr());   // associate file with file pointer object+    outfile.open(filename);            // associate file with file pointer object 
 +    //outfile.open(filename.c_str());   // convert filename to C-string if pre C++11
  
     if (!outfile)     if (!outfile)
Line 106: Line 107:
 #include <iostream> #include <iostream>
 #include <fstream> #include <fstream>
-#include <cstring>+#include <string>
 using namespace std; using namespace std;
  
 int main() int main()
 { {
-    const string filename = "some_numbers.txt";+    string filename = "some_numbers.txt";
     int num1;     int num1;
  
-    ifstream infile;   // instantiate file pointer object +    ifstream infile;         // instantiate file pointer object 
-    infile.open(filename.c_str());   // associate file with file pointer object +    infile.open(filename);   // associate file with file pointer object
-                                     // (file name needs to be a c_str)+
  
     if (!infile)     if (!infile)
-        cerr << "Error opening file." << endl; 
-    else 
     {     {
-        cout << "Reading from file ... ";+        cout << "Error opening file." << endl; 
 +        return 1;  // exit program with error code 
 +    } 
 +     
 +    cout << "Reading from file ... ";
  
-        infile >> num1; +    infile >> num1; 
-        infile.close();    // close the file!+    infile.close();    // close the file!
  
-        cout << "Done!" << endl; +    cout << "Done!" << endl; 
-        cout << "The first number in the file is " << num1 << "." << endl; +    cout << "The first number in the file is " << num1 << "." << endl;
-    }+
  
     return 0;     return 0;
Line 139: Line 140:
 #include <iostream> #include <iostream>
 #include <fstream> #include <fstream>
-#include <cstring>+#include <string>
 using namespace std; using namespace std;
  
 int main() int main()
 { {
-    const string filename = "some_numbers.txt";+    string filename = "some_numbers.txt";
     int num1, num2;     int num1, num2;
  
-    ifstream infile;   // instantiate file pointer object +    ifstream infile;         // instantiate file pointer object 
-    infile.open(filename.c_str());   // associate file with file pointer object+    infile.open(filename);   // associate file with file pointer object
  
     if (!infile)     if (!infile)
-        cerr << "Error opening file." << endl; 
-    else 
     {     {
-        cout << "Reading from file ... ";+        cout << "Error opening file." << endl; 
 +        return 1;  // exit program with error code 
 +    } 
 +     
 +    cout << "Reading from file ... ";
  
-        infile >> num1 >> num2; +    infile >> num1 >> num2; 
-        infile.close();    // close the file!+    infile.close();    // close the file!
  
-        cout << "Done!" << endl; +    cout << "Done!" << endl; 
-        cout << "The first two numbers in the file are:" << endl +    cout << "The first two numbers in the file are:" << endl 
-             << num1 << endl +         << num1 << endl 
-             << num2 << endl +         << num2 << endl 
-             << endl; +         << endl;
-    }+
  
     return 0;     return 0;
Line 174: Line 176:
 #include <iostream> #include <iostream>
 #include <fstream> #include <fstream>
-#include <cstring>+#include <string>
 using namespace std; using namespace std;
  
Line 182: Line 184:
     int num1;     int num1;
  
-    ifstream infile;   // instantiate file pointer object +    ifstream infile;         // instantiate file pointer object 
-    infile.open(filename.c_str());   // associate file with file pointer object+    infile.open(filename);   // associate file with file pointer object
  
     if (!infile)     if (!infile)
-        cerr << "Error opening file." << endl; 
-    else 
     {     {
-        cout << "Reading from file ... " << endl;+        cout << "Error opening file." << endl; 
 +        return 1;  // exit program with error code 
 +    }
  
-        while (infile >> num1) +    cout << "Reading from file ... " << endl;
-        { +
-            cout << num1 << endl; +
-        } +
-        infile.close();    // close the file!+
  
-        cout << "Done!" << endl;+    while (infile >> num1) 
 +    { 
 +        cout << num1 << endl;
     }     }
 +    infile.close();    // close the file!
 +
 +    cout << "Done!" << endl;
  
     return 0;     return 0;
 } }
 </file> </file>
cplusplus/file_processing_examples.txt · Last modified: 2019/02/11 19:17 by mithat
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