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PREAD
Section: Linux Programmer's Manual (2)Updated: 21 January 1999
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pread, pwrite - ¥Õ¥¡¥¤¥ë¡¦¥Ç¥£¥¹¥¯¥ê¥×¥¿¤ò»ØÄꤷ¤¿¥ª¥Õ¥»¥Ã¥È¤ÇÆɤ߽ñ¤¤¹¤ë½ñ¼°
#define _XOPEN_SOURCE 500#include <unistd.h>
ssize_t pread(int fd, void *buf, size_t count, off_t offset);
ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
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pread() ¤Ï¥Õ¥¡¥¤¥ë¡¦¥Ç¥£¥¹¥¯¥ê¥×¥¿¡¼ fd ¤Î(¥Õ¥¡¥¤¥ë¤ÎÀèƬ¤«¤é¤Î)¥ª¥Õ¥»¥Ã¥È offset ¤«¤éºÇÂç count ¥Ð¥¤¥È¤ò¥Ð¥Ã¥Õ¥¡ buf ¤ØÆɤ߹þ¤à¡£¥Õ¥¡¥¤¥ë¡¦¥ª¥Õ¥»¥Ã¥È¤ÏÊѲ½¤·¤Ê¤¤¡£pwrite() ¤Ï¥Ð¥Ã¥Õ¥¡ buf ¤«¤éºÇÂç count ¥Ð¥¤¥È¤ò¥Õ¥¡¥¤¥ë¡¦¥Ç¥£¥¹¥¯¥ê¥×¥¿¡¼ fd ¤Î¥ª¥Õ¥»¥Ã¥È offset ¤Ë½ñ¤¹þ¤à¡£¥Õ¥¡¥¤¥ë¡¦¥ª¥Õ¥»¥Ã¥È¤ÏÊѲ½¤·¤Ê¤¤¡£
fd ¤Ç»²¾È¤µ¤ì¤ë¥Õ¥¡¥¤¥ë¤Ï¥·¡¼¥¯(seek)¤¬²Äǽ¤Ç¤Ê¤±¤ì¤Ð¤Ê¤é¤Ê¤¤¡£
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À®¸ù¤·¤¿¾ì¹ç¡¢Æɤ߽ñ¤¤ò¹Ô¤Ã¤¿¥Ð¥¤¥È¿ô¤¬ÊÖ¤µ¤ì¤ë¡£(¥¼¥í¤Ï¡¢pwrite ¤Î¾ì¹ç¤Ë¤Ï²¿¤â½ñ¤«¤ì¤Ê¤«¤Ã¤¿¤³¤È¤ò°ÕÌ£¤¹¤ë¡£pread ¤Î¾ì¹ç¤Ë¤Ï¥Õ¥¡¥¤¥ë ¤ÎºÇ¸å¤Ë㤷¤¿¤³¤È¤ò°ÕÌ£¤¹¤ë) ¥¨¥é¡¼¤Î¾ì¹ç¤Ï -1 ¤¬ÊÖ¤µ¤ì¡¢ errno ¤¬¤½¤Î¥¨¥é¡¼¤ò¼¨¤¹¤è¤¦¤ËÀßÄꤵ¤ì¤ë¡£¥¨¥é¡¼
pread ¤Ç¤Ï read(2) ¤ª¤è¤Ó lseek(2) ¤Ç»ØÄꤵ¤ì¤¿Á´¤Æ¤Î¥¨¥é¡¼¤¬È¯À¸¤·¡¢ errno ¤òÀßÄꤹ¤ë²ÄǽÀ¤¬¤¢¤ë¡£ pwrite ¤Ç¤Ï write(2) ¤ª¤è¤Ó lseek(2) ¤Ç»ØÄꤵ¤ì¤¿Á´¤Æ¤Î¥¨¥é¡¼¤¬È¯À¸¤·¡¢ errno ¤òÀßÄꤹ¤ë²ÄǽÀ¤¬¤¢¤ë¡£½àµò
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pread ¤È pwrite ¥·¥¹¥Æ¥à¡¦¥³¡¼¥ë¤Ï Linux ¤Ë¥Ð¡¼¥¸¥ç¥ó 2.1.60 ¤Ç²Ã¤¨¤é¤ì¤¿¡£i386 ¤Î¥·¥¹¥Æ¥à¥³¡¼¥ë¤Î¥¨¥ó¥È¥ê¤Ï 2.1.69 ¤Ç²Ã¤¨¤é¤ì¤¿¡£ libc ¤Ë¤ª¤±¤ë¥µ¥Ý¡¼¥È¤Ï(¥·¥¹¥Æ¥à¥³¡¼¥ë¤ò»ý¤¿¤Ê¤¤¸Å¤¤¥«¡¼¥Í¥ë¤Ç¤Î ¥¨¥ß¥å¥ì¡¼¥·¥ç¥ó¤ò´Þ¤á¤Æ) glibc 2.1 ¤Ç²Ã¤¨¤é¤ì¤¿¡£´ØÏ¢¹àÌÜ
read(2), write(2), lseek(2)