Differences

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--- cplusplus:file_processing_examples [2013/03/01 01:19] – mithat
+++ cplusplus:file_processing_examples [2019/02/11 19:17] (current) – [Using filenames] mithat
@@ Line 42: / Line 42: @@
     if (!outfile)
-        cout << "Error opening file." << endl;
-    else
     {
-        cout << "Writing to the file ... ";
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with an error code
+    }
-        outfile << "KCMP\t" << 89.3 << endl;
+    cout << "Writing to the file ... ";
-        outfile << "KNOW\t" << 91.1 << endl;
-        outfile << "KSJN\t" << 99.5 << endl;
-        outfile.close();    // close the file!
-        cout << "Done!" << endl;
+    outfile << "KCMP\t" << 89.3 << endl;
-    }
+    outfile << "KNOW\t" << 91.1 << endl;
+    outfile << "KSJN\t" << 99.5 << endl;
+    outfile.close();    // close the file!
+    cout << "Done!" << endl;
     return 0;
@@ Line 59: / Line 60: @@
 </file>
-==== Filenames must be c_str ====
+==== Using filenames ====
 <file c++ simple-file-write3.cpp>// This program writes data to a file.
@@ Line 78: / Line 79: @@
     cin >> filename;
-    outfile.open(filename);   // 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 in pre-C++11
     if (!outfile)
+    {
         cout << "Error opening file." << endl;
-    else
+        return 1;  // exit program with an error code
+    }
+    cout << "Writing to the file ... ";
+    outfile << "KCMP\t" << 89.3 << endl;
+    outfile << "KNOW\t" << 91.1 << endl;
+    outfile << "KSJN\t" << 99.5 << endl;
+    outfile.close();    // close the file!
+    cout << "Done!" << endl;
+    return 0;
+}
+</file>
+===== File reading =====
+==== Simple example ====
+<file c++ simple-file-read.cpp>// This program reads a number from a file.
+#include <iostream>
+#include <fstream>
+#include <string>
+using namespace std;
+int main()
+{
+    string filename = "some_numbers.txt";
+    int num1;
+    ifstream infile;         // instantiate file pointer object
+    infile.open(filename);   // associate file with file pointer object
+    if (!infile)
     {
-        cout << "Writing to the file ... ";
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with error code
+    }
+    cout << "Reading from file ... ";
-        outfile << "KCMP\t" << 89.3 << endl;
+    infile >> num1;
-        outfile << "KNOW\t" << 91.1 << endl;
+    infile.close();    // close the file!
-        outfile << "KSJN\t" << 99.5 << endl;
-        outfile.close();    // close the file!
-        cout << "Done!" << endl;
+    cout << "Done!" << endl;
+    cout << "The first number in the file is " << num1 << "." << endl;
+    return 0;
+}
+</file>
+==== Reading multiple tokens ====
+<file c++ simple-file-read2.cpp>// This program reads two numbers from a file.
+#include <iostream>
+#include <fstream>
+#include <string>
+using namespace std;
+int main()
+{
+    string filename = "some_numbers.txt";
+    int num1, num2;
+    ifstream infile;         // instantiate file pointer object
+    infile.open(filename);   // associate file with file pointer object
+    if (!infile)
+    {
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with error code
     }
+    cout << "Reading from file ... ";
+    infile >> num1 >> num2;
+    infile.close();    // close the file!
+    cout << "Done!" << endl;
+    cout << "The first two numbers in the file are:" << endl
+         << num1 << endl
+         << num2 << endl
+         << endl;
     return 0;
@@ Line 98: / Line 172: @@
 </file>
-===== File reading =====
+==== Read all tokens in a file ====
+<file c++ simple-file-read3.cpp>// This program reads all the numbers from a file.
+#include <iostream>
+#include <fstream>
+#include <string>
+using namespace std;
+int main()
+{
+    const string filename = "some_numbers.txt";
+    int num1;
+    ifstream infile;         // instantiate file pointer object
+    infile.open(filename);   // associate file with file pointer object
+    if (!infile)
+    {
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with error code
+    }
+    cout << "Reading from file ... " << endl;
+    while (infile >> num1)
+    {
+        cout << num1 << endl;
+    }
+    infile.close();    // close the file!
+    cout << "Done!" << endl;
+    return 0;
+}
+</file>