read and write string in binary file
5 stars based on
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 to 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 structure.
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 visual c write binary data to file 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 the record we print the member x of that record. The only thing we need to explain visual c write binary data to file the fseek option. The function fseek must be declared like this:. The fseek function sets the file position indicator for the visual c write binary data to file 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 of 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 the 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 visual c write binary data to file 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 visual c write binary data to file 32 bits thus you see 01 00 00 00 in your hex-editor.
Try the following example visual c write binary data to file 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 test. 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 visual c write binary data to file have create because my true application i want manage.
Is this the right declaration of a binary file Binary files should visual c write binary data to file b in the visual c write binary data to file 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 to 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 pointers to list etc, and again want to set the same memory from this file. I want visual c write binary data to file store a character array data 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 the 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 following lines to the examples: This was an extremely helpful tutorial.
Thank you so much. I understand that fseek offsets the pointer by characters. LikeBe the first to […] kiran reddy on September 28th,