Basic file operation in C language: fopen, Fread, Fseek, fclose.

fopen

Function prototype FILE * fopen (const char *path,cost char *mode)

Action: Opens a file that returns a pointer to the file

Parameter description: The first parameter is the file path and file name to open the file, and the second parameter indicates how the file is opened

Note: Mode has the following values:

R: Read-only mode open, file must exist

r+: Readable and writable, must exist

rb+: Open binary file, you can read and write

rt+: Open text file, read and write

W: Write only, file exists the file length of 0, the file does not exist to create the file

w+: Can read and write, file exists The file length of 0, the file does not exist to establish the file

A: Attach the way to open only write, does not exist to create the file, there is written data added to the end of the file, the EOF character reserved

A +: Additional way to open to read and write, there is no establishment of the file, there is written data added to the end of the file, the EOF character does not retain

WB: Open binary file, write only

wb+: Open or set up binary files, read and write

wt+: Open or create a text file that can be read and written

at+: Open a text file, read-write, write data added to the end of the text

ab+: Open binary files, read and write, written data added to the end of the file

By the mode character, the above example, R, W, a can be followed by a B, which means that the file is opened in binary form

Return value: The file opens, returning a pointer to the open file (file structure), failure to open files, error code (error codes)

Note: After the fopen operation to be judged, whether the file is open, the file is actually open to do the following read or write operations, if there are errors to be handled incorrectly

Example: FILE *pfile=fopen (const char *filename, "RB");

Open file stream There is also a function that supports wide characters, as follows

FILE *_wfopen (const wchar_t *filename,const wchar_t *mode)

fread

Function prototype: size_t fread (void* buff,size_t size,size_t count,file* Stream)

Function: Reads data from a file into a specified address

Parameters: The first parameter is the pointer to the data (buff), or the address of the data store

The second parameter is the size of a single element, the size of the data that is written to the address by the pointer, and the unit is byte

The third parameter is the number of elements, that is, the element that is the size of the data to be read

The fourth parameter is the file pointer that provides the data, which points to the file's internal data

Return value: Number of total data elements read

Cases:

int num,count;

int* Pr=new Int[num*count];

Fread (PR, num*4, Count, stream); Stream is the file pointer returned in fopen

To write data to PR, you must allocate memory for PR, one int is 4 bytes, so be x4

fseek

Function prototype: int fseek (FILE *stream,long offset,int framewhere)

Role: Reposition a pointer inside a file

Parameters: The first is the file pointer, the second is the pointer offset, and the third is the pointer offset starting position

Return value: Relocation successfully returns 0, otherwise it returns a value other than 0

It is important to note that the function is not to reposition the file pointer, but to reposition the pointer inside the file so that pointers to the internal data in the file are moved to the data in the file that we are interested in, which is primarily the purpose of relocation.

Note: Execution succeeded, then the stream points to the position of offset bytes based on Fromwhere. Execution failed (for example, if offset offset is outside the file size), keep the original stream position unchanged

fclose

Function prototype: int fclose (FILE *stream)

Function: Closes a file stream, using fclose to output the last remaining data in the buffer to the disk file and releasing the file pointer and related buffers

Proficient use of the above four functions can be obtained from the file to our useful data type, the premise for the file format is very understanding, for example, for a DIB bitmap file, you can read out his files in the header and pixel information.