Source Code : File HAndling In C

File Handling

Files let you store data on secondary storage such as a hard disk so that your programs can later retrieve that data again. There are 2 types of files which are text files and data files.

•Text files are used for storing character strings in a file. To create a text file you must first declare a file pointer.

•You must then open the file using the fopen function. fopen takes 2 parameters which are the file name and the open mode. fopen returns a file pointer which we will assign to the file pointer called f.

•To write a string to the file you must use the fprintf command. fprintf is just like printf except that you must use the file pointer as the first parameter.

•When you are finished using a file you must always close it. If you do not close a file then some of the data might not be written to it. Use the fclosecommmand to close a file

#include
int main()
{ FILE *f;
f = fopen("test.txt","w");fprintf(f,"Hello");fclose(f);
return 0;

}

The fgets command is used when reading from a text file. You must first declare a character array as a buffer to store the string that is read from the file. The 3 parameters for fgets are the buffer variable, the size of the buffer and the file pointer.

#include
int main()
{

FILE *f;
char buf[100];
f = fopen("test.txt","r");fgets(buf,sizeof(buf),f);fclose(f);printf("%s\n",buf);
return 0;

}

Data files

A data file is used to store types of data such as integers. When you open a data file you must add the letter b to the open mode parameter of fopen.

fwrite is used to write to a file. The first parameter of fwrite is a pointer to the variable that you want to write to the file. The second parameter is the size of the variable that must e written. The third parameter is the number of variables to be written. The fourth parameter is the file pointer of the file you want to write to.

fread is used to read from a file and is the same as fwrite except that the data is read into the variable instead of writing from it. You must remember to change the file mode to read.

#include
int main()
{ FILE *f;intbuf;
f = fopen("test.dat","wb");buf = 100;fwrite(&buf,sizeof(buf),1,f);fclose(f);
return 0;

}

#includestruct
{ char name[100];int age;

} p;
int main()
{

FILE *f;strcpy(p.name,"John");p.age = 25;
f = fopen("test.dat","wb");fwrite(&p,1,sizeof(p),f);fclose(f);

return 0; 
}

Procedures

Procedure is a function whose return type is void

Functions will have return types int, char, double, float or even structs and arrays

Return type is the data type of the value that is returned to the calling point after the called function execution completes

Functions and Parameters

Syntax of function

Declaration section

<> funname(parameter list);

Definition section

<> funname(parameter list)

{

  body of the function

}

Function Call

Funname(parameter);

Call by Value

Calling a function with parameters passed  as values

int a=10;  void fun(int a)

fun(a);    {

  defn;

  }

Here fun(a) is a call by value.

Any modification done with in the function is local to it and will not be effected outside the function

Example program – Call by value

#include

void main()

{

  int a=10;

  printf(“%d”,a);  a=10

  fun(a);

  printf(“%d”,a);  a=10

}

void fun(int x)

{

  printf(“%d”,x)  x=10

  x++;

  printf(“%d”,x);  x=11

}

Call by reference

Calling a function by passing pointers as parameters (address of variables is passed instead of variables)

int a=1;  void fun(int *x)

fun(&a);    {

  defn;

  }

Any modification done to variable a will effect outside the function also