The Basics of C Programming

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In this C programming tutorial we are going to talk about the use of binary files. Binary files are very similar to arrays of structures, except the structures are in a disk-file rather than an array in memory. Binary files have two features that distinguish them from text files: After you have opened the binary file, you can read and write a structure or seek a specific position in the file. A file position indicator points c write binary data to text file record 0 when the file is opened.

A read operation reads the structure where the file position indicator is pointing to. After reading the structure the pointer is moved to point at the next structure. A write operation will write to the currently pointed-to structure. After the write operation the file position indicator is moved to point at the next c write binary data to text file.

Remember that you keep track of things, because the file position indicator can not only point at the beginning of a structure, but can also point to any byte in the file.

Only one block is requested. Changing the one into ten will read in ten blocks of x bytes at once. In this example we declare a structure rec with the members x,y and z of the type integer.

In the main function we open fopen a file for writing w. Then we check if the file is open, if not, an error message is displayed and we exit the program. Then we write the record to the file. We do this ten times, thus creating ten records. Take a look at the example:. With the fread we read-in the records one by one. After we have read c write binary data to text file record we print the member x of that record.

The only thing we need to explain is the fseek option. The function fseek must be declared like this:. The fseek function sets the file position indicator for the stream pointed to by the stream. The new position, measured in characters from the beginning of the file, is obtained by adding offset to the position specified by whence. Three macros are declared in stdio.

Using negative numbers it is possible to move from the end c write binary data to text file the file. In this example we are using fseek to seek the last record in the file. This counter is then used in the fseek statement to set the file pointer at the desired record.

The result is that we read-in c write binary data to text file records in the reverse order. The function rewind can be used like this:. With the fseek statement in this example we go to the end of the file. Then we rewind to first position in the file. Then read-in all records and print the value of member x.

Without the rewind you will get garbage. The int types must contain at least 16 bits to hold the required range of values. But it also can vary per compiler and the platform you are compiling for. On compilers for 8 and 16 bit processors including Intel x86 processors executing in 16 bit mode, such as under MS-DOSan int is usually 16 bits and has exactly the same representation as a short.

On compilers for 32 bit and larger processors including Intel x86 processors executing in 32 bit mode, such as Win32 or Linux an int is usually 32 bits long and has exactly the same representation as a long. A int holds 32 bits thus you see 01 00 00 00 in your hex-editor. Try the following example to see the sizeof variable types for your target platform: So if you want to see only one byte in your hex editor, change the program to this: If you open the file c write binary data to text file.

Or if you want to use int, accept that 4 bytes are written in the binary file but at least you know now why this is.

Hi, after piratical and try to understanding write and read, my write is perfect what i want, but i can not read my bin file, i need some help please. I have tested them and they work, so good luck! Hi, Tanks for your help and support, my last message with my binary writer test, is perfect for me, because i can write a hex value directly in file00 to FF anywhere i want in file, but i cant read it with fread after, i want practice this with a small file i have create because my true application i want manage.

Is this the right declaration of a binary file Binary files should have b in the mode e. You are right, if you only look at the syntax.

But if you open test. But to keep the syntax correct, we have changed the source code examples. The modes you can use are as follows: Is there a possibility to deal with data packing of the compiler in the structure, because due to this structure members are not necessarily continuous in the memory. And mention that you get garbage without the rewind. If you seek c write binary data to text file the end of file and then offset beyond the end of the file, you will be reading garbage, you need a negative offset.

The search for the end of the file is only done, so we that we can rewind. I want to dump some memory into a file, a complex structure which contains c write binary data to text file to list etc, and again want to set the same memory from this file. I want to store a character array c write binary data to text file 89 bytes to a binary file.

Please send the fwrite function code for this. Is it possible to store current PC time to same binary file? You just have to add some additional lines.

The examples now only uses the variable x to keep the examples smaller. To use all three x,y,z variables add the following lines to c write binary data to text file examples:. Please enlighten me with your wisdom, great one. LikeBe the first to […]. Thanks a lot for the kind help. It really helped me to my aim what I was finding. Thanks again… Have happy programming…! Can you add another program of telling how to add and delete records at particular positions.?

Hello I am trying to read satellite CEOS format file which contacined all type of data like integer ascii,binary. I know structure of binary file. I am reading file according to structure but not able to display data. Is it require after reading data structure-wise to conver binary to decimal format?

I want to know how. Binary files Binary files are very similar to arrays of structures, except the structures are in a disk-file rather than an array in memory. You can instantly use any structure in the file. You can change the contents of a structure anywhere in the file. The fseek function will move the file position indicator to the record that is requested. The fread and fwrite function takes four parameters: A memory address Number of bytes to read per block Number of blocks to read A file variable For example: This entry was posted in C Tutorials.

You can follow any responses to this entry through the RSS 2. Both comments and pings are currently closed. Hope that this answers your question! Tanks again selewa on July 29th, Good luck and thx for correcting us! Martin on July 30th, Hi, Is there a possibility to deal with data packing of the compiler in the structure, because due to this structure members are not necessarily continuous in the memory.

Now, if you want to read the 5 bytes from your binary file using: Is there any method to prevent this?? John on August 6th, These 2 lines are pointless in your example. Or am I mistaken? Pratap on January 22nd, Thanks, Sandeep mohammed on May 13th, To use all three x,y,z variables add the c write binary data to text file lines to the examples: This was an extremely helpful tutorial. Thank you so much. I understand that fseek offsets the pointer by characters.

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Up to this point, we have been using text mode to read and write data to and from the file. In this chapter, we will learn how we can read and write data to and from the file using the binary mode. Recall that in binary mode data is stored in the file in the same way as in the memory, so no transformation of data takes place in binary mode.

As no transformation takes place binary mode is significantly faster than text mode. Although we can also use them with text mode too.

On success, it returns the count of the number of items successfully written to the file. On error, it returns a number less than n. Let's say we don't' want to write all elements of the array into the file, instead, we want is to write only 0th and 1st element of the array into the file. Now you have understood how fwrite function works. Let's create a program using fwrite function. In lines , a structure employee is declared which has four members namely name is an array of characters, designation is also an array of characters, age is of type int and salary is of type float.

Along with the structure definition, a variable emp of type struct employee is also declared. In line 17, fopen function is called with two arguments namely "employee.

On success, it returns a pointer to file employee. On failure, it returns NULL. In lines , if statement is used to test the value of fp. If it is NULL, printf statement prints the error message and program terminates. Otherwise, the program continues with the statement following the if statement.

In lines , the statements in the for loop asks the user to enter four pieces of information namely name, designation, age and salary. Notice that in line 34 fflush function is called to flush remove the newline character from the standard input which was entered while entering the number of records in line If there had been no call to fflush stdin then gets function in line 37 would have read the newline character from the standard input and doesn't wait for user input.

In line 48, fwrite function is called to write the structure variable emp into the file in binary mode. We already know that on success fwrite returns the number of items written to the file. Here we are writing the data of a single structure variable so fwrite will return 1.

On error, it will return a number less than 1. The return value of fwrite is then assigned to the chars variable. In line 49, the printf statement prints the number of items successfully written to the file.

Let's start with fwrite function. It specifies the number of bytes of each item to be written. It is the number of items to be written. It is a pointer to the file where data items will be written. To better understand fwrite function consider the following examples: The following program demonstrates how to use fwrite function. Enter the number of records you want to enter: In line 14, three variables n, i and chars are declared of type int.

In line 15, a structure pointer fp of type struct FILE is declared. In line 52, fclose function is used to close the file.