[Tutorial] Standard I/O - Page 3

aaroncohn · #21 27-Feb-2004, 22:07

Standard I/O - Example #3 (Windows)

This example creates a binary file of structures. The application is a windows application. The screen will have five input boxes: name, social security number, age, and gpa. There is a save button on the screen. When the user fills in all input boxes and clicks the save button, the application places the data in a structure and writes the structure to a binary file. If the file has other structures in it, the new structure is appended at the end of the file.

CPP / C++ / C Code:

#include <stdio.h>
#include <string.h>

#define NAMESIZE 10
#define SSNSIZE  11

typedef struct
{
  char  name[NAMESIZE+1];
  char  ssn[SSNSIZE+1];
  int   age;
  float gpa;
  float salary;
}PERSON;

void __fastcall StudentDataForm::SaveBtnClick(TObject *Sender)
{
  int    result;
  PERSON student;
  FILE  *binfile;

  // get the data from the Edit boxes.
  strcpy(student.name, Name->Text.c_str());
  strcpy(student.ssn, SSN->Text.c_str());
  student.age = atoi(Age->Text.c_str());
  student.gpa = atof(GPA->Text.c_str());
  student.salary = atof(Salary->Text.c_str());
  
  // open the file in binary append mode
  if ((binfile = fopen("c:\\data.dat","ab") == NULL)
    MessageBox(NULL,"Cannot open output file.",NULL,0);
  else
    if (fwrite(&student,sizeof(PERSON),1,binfile) != 1)
      MessageBox(NULL,"Cannot write data to the file.",NULL,0);

  fclose(binfile);
  return 0;
}

In this example we get the data from the edit boxes. We assume in this example that we have designed this program to be robust and that there can only be valid data in the edit boxes.

Once the data has been stored in the structure, we open the output file in append mode in binary format. If the opening of the file succeeded, we write (append) the structure to the file. We then close the file. If there is a problem either opening the file or writing to the file, we have an error window displayed.

Always remember that failing to test all file I/O will result in poor code, poor execution, and unhappy customers.

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To discuss this tutorial: please follow the discussion here http://www.gidforums.com/t-2632.html.

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