There is also a variant of seekp that allows you to specify a position relative to the current put pointer location, or relative to the end of the file. This counter is then used in the fseek statement to set the file pointer at the desired record.
Getting The Size of a File The typical way to get the size of a file is to use the C library function stat: The current reading position, which is the index of the next byte that will be read from the file. If the put pointer is current at the end of the file, the file is extended.
The result is that we read-in the records in the reverse order. Binary files have two features that distinguish them from text files: You can instantly use any structure in the file.
If an error occurs while reading for example, if you read off the end of a filethe stream is placed in an error state.
You can read or write complex data objects using simple type casting of pointers: If the put pointer points into the middle of the file, characters in the file are overwritten with the new data. To correct this, ensure constants used in file positioning are long quantities, or that all variables used in such positioning are long quantities, or both.
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 determine the current put pointer position using "myFile. This is called the "get pointer" since it points to the next character that the basic get method will return.
The function fseek must be declared like this: The above example shows the use of a local variable to hold the results returned by stat. You can follow any responses to this entry through the RSS 2.
Then we write the record to the file. There is also a variant of seekg that allows you to specify a position relative to the current get pointer location, or relative to the end of the file. It is your responsibility to create and manage the memory where read will place its result, as well as to ensure that it is large enough to hold the number of bytes requested.
The new position, measured in characters from the beginning of the file, is obtained by adding offset to the position specified by whence. Without the rewind you will get garbage. The current writing position, which is the index of the byte location where the next output byte will be placed.
Then we check if the file is open, if not, an error message is displayed and we exit the program. If that occurs, you can use the gcount method to find out the number of characters that were actually read, and use the clear method to reset the stream to a usable state. Opening a File A file stream object can be opened in one of two ways.
With the fread we read-in the records one by one. You can determine the current get pointer position using "myFile. For convenience, the "array" of bytes stored in a file is indexed from zero to len-1, where len is the total number of bytes in the entire file.
The fread and fwrite function takes four parameters: Then we rewind to first position in the file.
A write operation will write to the currently pointed-to structure.Normally, for binary file i/o you do not use the conventional text-oriented > operators! It can be done, but that is an advanced topic. Although the read and write methods accept a char* pointer, there is no requirement that the data you read and/or write be held in a char array.
You can read or write complex data objects using. Mar 31, · I've made an array of structures. I did so by making an pointer to an array of pointers (by dynamic allocation),and allocate the address of a structure to one of these last pointers.
Everything should be written to a binary file. I have a char type array with bytes stored in it.
I want to write this char type byte array to a file. How could I do this? I am not writing to. 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. There are currently 32 responses to “C Tutorial – Binary File I/O” I want to store a character array data (89 bytes) to a binary file.
Please send. The easiest way to create binary files is to use fixed-length character arrays instead of std::string. That will make each of the records in the binary fine the same size and you can easily locate any record in the file by simply multiplying.
You could rely on the '\0' marker that is guaranteed to be at the end of a c-string or the equivalent string::c_str() call, but that is not a good idea because 1. you have to read in the string character by character checking for the null 2.
a std::string can legitimately contain a null byte (although it really shouldn't because calls to c_str.Download