文件操作fopen, fclose, fread, fwrite, fseek, ftell
fopen
FILE * fopen ( const char * filename, const char * mode );
fclose
int fclose ( FILE * stream );
fread
size_t fread ( void * ptr, size_t size, size_t count, FILE * stream );
Read block of data from stream
Reads an array of
count elements, each one with a size of
size bytes, from the
stream and stores them in the block of memory specified by
ptr.
The position indicator of the stream is advanced by the total amount of bytes read.
The total amount of bytes read if successful is (size*count).
fwrite
size_t fwrite ( const void * ptr, size_t size, size_t count, FILE * stream );
Write block of data to stream
Writes an array of
count elements, each one with a size of
size bytes, from the block of memory pointed by
ptr to the current position in the
stream.
The position indicator of the stream is advanced by the total number of bytes written.
Internally, the function interprets the block pointed by ptr as if it was an array of
(size*count) elements of type
unsigned char, and writes them sequentially to stream as if fputc was called for each byte.
fseek
int fseek ( FILE * stream, long int offset, int origin );
Reposition stream position indicator
Sets the position indicator associated with the
stream to a new position.
For streams open in binary mode, the new position is defined by adding offset to a reference position specified by origin.
For streams open in text mode, offset shall either be zero or a value returned by a previous call to ftell, and origin shall necessarily be SEEK_SET.
If the function is called with other values for these arguments, support depends on the particular system and library implementation (non-portable).
The end-of-file internal indicator of the stream is cleared after a successful call to this function, and all effects from previous calls to ungetc on this stream are dropped.
On streams open for update (read+write), a call to fseek allows to switch between reading and writing.
Parameters
- stream
- Pointer to a FILE object that identifies the stream.
- offset
-
Binary files: Number of bytes to offset from
origin.
Text files: Either zero, or a value returned by ftell. - origin
-
Position used as reference for the
offset. It is specified by one of the following constants defined in
exclusively to be used as arguments for this function:
* Library implementations are allowed to not meaningfully support SEEK_END (therefore, code using it has no real standard portability).Constant Reference position SEEK_SET Beginning of file SEEK_CUR Current position of the file pointer SEEK_END End of file *
ftell
long int ftell ( FILE * stream );
Get current position in stream
Returns the current value of the position indicator of the
stream.
For binary streams, this is the number of bytes from the beginning of the file.
For text streams, the numerical value may not be meaningful but can still be used to restore the position to the same position later using fseek (if there are characters put back using ungetc still pending of being read, the behavior is undefined).
参考资料
http://www.cplusplus.com/