Linux Certif

Toute la documentation sur la certification Linux LPI

lseek

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lseek - ¥Õ¥¡¥¤¥ë¤ÎÆɤ߽ñ¤­¥ª¥Õ¥»¥Ã¥È¤Î°ÌÃÖ¤òÊѤ¨¤ë

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#include <sys/types.h>
#include <unistd.h>

off_t lseek(int fildes, off_t offset, int whence);

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lseek() ´Ø¿ô¤Ï¡¢¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿ (descriptor) fildes ¤ËÂбþ¤¹¤ë¥ª¡¼¥×¥ó¤µ¤ì¤¿¥Õ¥¡¥¤¥ë¤Î¥ª¥Õ¥»¥Ã¥È¤ò¡¢ whence ¤Ë´ð¤Å¤­ offset °ú¤­¿ô¤Î°ÌÃ֤ذʲ¼¤Î¤è¤¦¤ËÊѹ¹¤¹¤ë:

SEEK_SET

¥ª¥Õ¥»¥Ã¥È¤Ï offset ¥Ð¥¤¥È¤ËÀßÄꤵ¤ì¤ë¡£

SEEK_CUR

¥ª¥Õ¥»¥Ã¥È¤Ï¸½ºß°ÌÃÖ¤Ë offset ¥Ð¥¤¥È¤ò­¤·¤¿°ÌÃ֤ˤʤ롣

SEEK_END

¥ª¥Õ¥»¥Ã¥È¤Ï¥Õ¥¡¥¤¥ë¤Î¥µ¥¤¥º¤Ë offset ¥Ð¥¤¥È¤ò­¤·¤¿°ÌÃ֤ˤʤ롣

lseek() ´Ø¿ô¤Ï¡¢¥ª¥Õ¥»¥Ã¥È¤ò¥Õ¥¡¥¤¥ë¤ÎËöÈø¤ò±Û¤¨¤¿°ÌÃÖ¤ËÀßÄê¤Ç¤­¤ë (⤷¡¢¤³¤ì¤Ë¤è¤ê¥Õ¥¡¥¤¥ë¤Î¥µ¥¤¥º¤¬ÊѤï¤é¤Ê¤¤)¡£ ¤â¤·¥Ç¡¼¥¿¤¬¤³¤Î¥ª¥Õ¥»¥Ã¥È°ÌÃְʹߤ˽ñ¤­¹þ¤Þ¤ì¤¿¾ì¹ç¡¢ ´Ö¤Î¶õ·ä¤ÎÉôʬ ("·ê (hole)") ¤ÎÆɤ߽Ф·¤¬¤¢¤ë¤È¡¢ ¼ÂºÝ¤Ë¤½¤³¤Ë¥Ç¡¼¥¿¤ò½ñ¤­¹þ¤Þ¤ì¤ë¤Þ¤Ç¤Ï NULL ¥Ð¥¤¥È ('\0') ¤ÎÎó¤¬ÊÖ¤µ¤ì¤ë¡£

ÊÖ¤êÃÍ

À®¸ù¤·¤¿¾ì¹ç¡¢ lseek() ¤Ï·ë²Ì¤Î¥Õ¥¡¥¤¥ë°ÌÃÖ¤ò¥Õ¥¡¥¤¥ë¤ÎÀèƬ¤«¤é¤Î¥Ð¥¤¥È¿ô¤ÇÊÖ¤¹¡£ ¥¨¥é¡¼¤Î¾ì¹ç¡¢ÃͤȤ·¤Æ (off_t)-1 ¤òÊÖ¤·¡¢ errno ¤Ë¥¨¥é¡¼¤¬»Ø¼¨¤µ¤ì¤ë¡£

¥¨¥é¡¼

EBADF

fildes ¤¬¥ª¡¼¥×¥ó¤µ¤ì¤¿¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Ç¤Ê¤¤¡£

EINVAL

whence ¤¬ SEEK_SET, SEEK_CUR, SEEK_END ¤Î¤É¤ì¤Ç¤â¤Ê¤¤¡£ ¤Þ¤¿¤Ï¡¢seek ¤Î·ë²Ì¡¢¥Õ¥¡¥¤¥ë¡¦¥ª¥Õ¥»¥Ã¥È¤¬Éé¤Ë¤Ê¤Ã¤Æ¤·¤Þ¤¦¤«¡¢ seek ²Äǽ¤Ê¥Ç¥Ð¥¤¥¹¤ÎËöÈø¤ò±Û¤¨¤Æ¤·¤Þ¤¦¡£ EOVERFLOW ·ë²Ì¤Î¥Õ¥¡¥¤¥ë¡¦¥ª¥Õ¥»¥Ã¥È¤ò off_t ·¿¤Çɽ¸½¤¹¤ë¤³¤È¤¬¤Ç¤­¤Ê¤¤¡£

ESPIPE

fildes ¤¬¥Ñ¥¤¥×¡¢¥½¥±¥Ã¥È¡¢FIFO ¤ò»²¾È¤·¤Æ¤¤¤ë¡£

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SVr4, 4.3BSD, POSIX.1-2001.

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¤³¤Îʸ¾Ï¤Ç»ÈÍѤ·¤¿ whence ¤Ï±Ñ¸ì¤È¤·¤ÆÀµ¤·¤¯¤Ê¤¤¤¬¡¢ Îò»ËŪÍýͳ¤Ë¤è¤ê¤½¤Î¤Þ¤Þ»È¤ï¤ì¤Æ¤¤¤ë¡£

¤¤¤¯¤Ä¤«¤Î¥Ç¥Ð¥¤¥¹¤Ç¤Ï seek ¤¬¤Ç¤­¤Ê¤¤¡£ POSIX ¤Ï¤É¤Î¥Ç¥Ð¥¤¥¹¤¬ lseek() ¤ËÂбþ¤¹¤Ù¤­¤«¤Ïµ¬Äꤷ¤Æ¤¤¤Ê¤¤¡£

Linux ¤Ç¤Ï¡¢ tty ¥Ç¥Ð¥¤¥¹¤Ë lseek() ¤ò»ÈÍѤ¹¤ë¤È ESPIPE ¤òÊÖ¤¹¡£

¸Å¤¤¥³¡¼¥É¤òÊÑ´¹¤¹¤ë»þ¤Ï whence ¤ÎÃͤò°Ê²¼¤Î¥Þ¥¯¥í¤ËÃÖ¤­´¹¤¨¤ë¤³¤È:

old	new
0	SEEK_SET
1	SEEK_CUR
2	SEEK_END
L_SET	SEEK_SET
L_INCR	SEEK_CUR
L_XTND	SEEK_END

ÊÖ¤êÃͤη¿¤Ï¡¢SVr1-3 ¤Ç¤Ï off_t ¤Ç¤Ï¤Ê¤¯ long ¤Ç¤¢¤ê¡¢ BSD ¤Ç¤Ï int ¤Ç¤¢¤ë¡£

dup(2) ¤ä fork(2) ¤ÇºîÀ®¤µ¤ì¤¿¥Õ¥¡¥¤¥ë¥Ç¥£¥¹¥¯¥ê¥×¥¿¤Ï¡¢¸½ºß¤Î¥Õ¥¡¥¤¥ë°ÌÃ֥ݥ¤¥ó¥¿ (current file position pointer) ¤ò¶¦Í­¤·¤Æ¤¤¤ë¤Î¤Ç¡¢ ¤³¤Î¤è¤¦¤Ê¥Õ¥¡¥¤¥ë¤Ç°ÜÆ°¤ò¹Ô¤¦¤È¶¥¹ç¾õÂÖ¤ò°ú¤­µ¯¤³¤¹²ÄǽÀ­¤¬¤¢¤ë¡£

´ØÏ¢¹àÌÜ

dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3)