12. stdio의 동작 확인

cat2.c 프로그램을 strace로 조사해보자.

 

stdio 버퍼링 확인)

dev@dev-desktop:~/codeexample$ strace -e trace=open,read,write,close ./cat data >/dev/null
close(3)                                = 0
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200l\2\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 2048
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 2048) = 1418
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 1418) = 1418
read(3, "", 2048)                       = 0
close(3)                                = 0
+++ exited with 0 +++
dev@dev-desktop:~/codeexample$ strace -e trace=open,read,write,close ./cat2 data >/dev/null
close(3)                                = 0
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200l\2\0\0\0\0\0"..., 832) = 832
close(3)                                = 0
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
read(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 1418
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 4096) = 4096
read(3, "", 4096)                       = 0
close(3)                                = 0
write(1, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 1418) = 1418
+++ exited with 0 +++

 

같은 aaa로 도배된 파일이지만 버퍼링때문에 읽기와 쓰기 횟수가 다르다.