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分享feek()函数
函数调用
feek(fp,10L,2);这个2代表代表seek_end?
另外如果是代表文件结尾，再向前移动10个字节会到哪里啊。
seek_set是0，seek_cur是1，seek_end是2，是这个顺序吧？ 求大神指点
feek(fp,10L,2);这个2代表代表seek_end?
另外如果是代表文件结尾，再向前移动10个字节会到哪里啊。
seek_set是0，seek_cur是1，seek_end是2，是这个顺序吧？ 求大神指点
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Rookiekk 2017-03-15
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谢谢老鼠
赵4老师 2017-03-15
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fseek
Moves the file pointer to a specified location.
int fseek( FILE *stream, long offset, int origin );
Function Required Header Compatibility
fseek <stdio.h> ANSI, Win 95, Win NT
For additional compatibility information, see Compatibility in the Introduction.
Libraries
LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version
Return Value
If successful, fseek returns 0. Otherwise, it returns a nonzero value. On devices incapable of seeking, the return value is undefined.
Parameters
stream
Pointer to FILE structure
offset
Number of bytes from origin
origin
Initial position
Remarks
The fseek function moves the file pointer (if any) associated with stream to a new location that is offset bytes from origin. The next operation on the stream takes place at the new location. On a stream open for update, the next operation can be either a read or a write. The argument origin must be one of the following constants, defined in STDIO.H:
SEEK_CUR
Current position of file pointer
SEEK_END
End of file
SEEK_SET
Beginning of file
You can use fseek to reposition the pointer anywhere in a file. The pointer can also be positioned beyond the end of the file. fseek clears the end-of-file indicator and negates the effect of any prior ungetc calls against stream.
When a file is opened for appending data, the current file position is determined by the last I/O operation, not by where the next write would occur. If no I/O operation has yet occurred on a file opened for appending, the file position is the start of the file.
For streams opened in text mode, fseek has limited use, because carriage return–linefeed translations can cause fseek to produce unexpected results. The only fseek operations guaranteed to work on streams opened in text mode are:
Seeking with an offset of 0 relative to any of the origin values.
Seeking from the beginning of the file with an offset value returned from a call to ftell.
Also in text mode, CTRL+Z is interpreted as an end-of-file character on input. In files opened for reading/writing, fopen and all related routines check for a CTRL+Z at the end of the file and remove it if possible. This is done because using fseek and ftell to move within a file that ends with a CTRL+Z may cause fseek to behave improperly near the end of the file.
Example
/* FSEEK.C: This program opens the file FSEEK.OUT and
* moves the pointer to the file's beginning.
*/
#include <stdio.h>
void main( void )
{
FILE *stream;
char line[81];
int result;
stream = fopen( "fseek.out", "w+" );
if( stream == NULL )
printf( "The file fseek.out was not opened\n" );
else
{
fprintf( stream, "The fseek begins here: "
"This is the file 'fseek.out'.\n" );
result = fseek( stream, 23L, SEEK_SET);
if( result )
perror( "Fseek failed" );
else
{
printf( "File pointer is set to middle of first line.\n" );
fgets( line, 80, stream );
printf( "%s", line );
}
fclose( stream );
}
}
Output
File pointer is set to middle of first line.
This is the file 'fseek.out'.
Stream I/O Routines
See Also ftell, _lseek, rewind
赵4老师 2017-03-15
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到了结尾下边10个字节的地方
www_adintr_com 2017-03-14
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如果你是写文件, 文件的长度会自动扩展, 中间的部分内容当做 0
在 UNIX 下, 利用这种方式可以制作文件空洞, 就是文件实际占用的磁盘空间比文件的大小更小.
自信男孩 2017-03-14
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int fseek(FILE * stream, long offset, int whence);Rookiekk 2017-03-14
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老师您好，我已经了解了那几个词的定义。但是在文件结尾再向前移动10个字节，那个位置到哪里了呢？是到了结尾下边10个字节的地方，还是会自动回到开头在移动10个字节呢？
Rookiekk 2017-03-14
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老师您好，我已经了解了那几个词的定义。但是在文件结尾再向前移动10个字节，那个位置到哪里了呢？是到了结尾下边10个字节的地方，还是会自动回到开头在移动10个字节呢？
赵4老师 2017-03-14
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VS IDE中，在不明白的符号上点鼠标右键，选转到定义。
