C Binary File Read

C Binary File Read

What is binary file ?

Unformatted data file organises data into blocks containing continuous bytes of information.

Blocks represents the more complex data structures such as arrays of structures.

C programming language provides the built-in functions for file processings.

We can read the binary file using any of the following file modes based on the requirements,

r -> used to open file for reading and position at the start of the file.

r+ -> used to open file for update (both reading and writing), initial position is at the start of the file for reading and writing.

w+ -> used to open file for update (both reading and writing) and new file is created if file does not exists, initial position is at the start of the file for reading and writing

a+ -> used to open file for update (both reading and writing), initial position is at the end of the file for reading and writing.

C program to read bnary file

This c program is used to read the binary file and assign values to structure variable student id, name and mark using file read mode then prints all the records in the file.

student_id, student_name and mark are part of structure variable student and reads the file 'student_mark_list.txt'.

#include<stdio.h>                                                          
                                                                                
struct student                                                                  
{                                                                               
 char name[30];                                                                 
 int id, mark;                                                                  
};                                                                              
void main()                                                                     
{                                                                               
  struct student stu;                                                           
  FILE *fp;                                                                     
  fp = fopen("student_mark_list.txt", "ab+");                                   
  if(fp == NULL)                                                                
  {                                                                             
    printf("\nInvalid binary file!");                                           
  }                                                                             
  else                                                                          
  {                                                                             
     printf("\nStudent mark details");                                          
     printf("\n---------------------");                                         
     printf("\nstudent id\tstudent name\t mark");                               
     while(fread(&stu, sizeof(stu),1,fp)==1)                                    
     {                                                                          
       printf("\n%d\t%s\t%d", stu.id,stu.name,stu.mark);                        
     }                                                                          
     fclose(fp);                                                                
  }                                                                             
}  

Assume binary file 'student_mark_list.txt' content :

$ cat student_mark_list.txt 
student1p@p@
Ystudent2p@p@Cstudent3p@p@b

Output:

$ cc binary-file-read.c 
$ ./a.out 

Student mark details
---------------------
student id	student name	 mark
1	student1	89
2	student2	67
3	student3	98