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25 .TH SOCKATMARK 3 2021-03-22 "Linux" "Linux Programmer's Manual"
27 sockatmark \- determine whether socket is at out-of-band mark
30 .B #include <sys/socket.h>
32 .BI "int sockatmark(int " sockfd );
36 Feature Test Macro Requirements for glibc (see
37 .BR feature_test_macros (7)):
42 _POSIX_C_SOURCE >= 200112L
46 returns a value indicating whether or not the socket referred
47 to by the file descriptor
49 is at the out-of-band mark.
50 If the socket is at the mark, then 1 is returned;
51 if the socket is not at the mark, 0 is returned.
52 This function does not remove the out-of-band mark.
56 returns 1 if the socket is at the out-of-band mark, or 0 if it is not.
57 On error, \-1 is returned and
59 is set to indicate the error.
64 is not a valid file descriptor.
67 .\" POSIX.1 says ENOTTY for this case
69 is not a file descriptor to which
74 was added to glibc in version 2.2.4.
76 For an explanation of the terms used in this section, see
84 Interface Attribute Value
87 T} Thread safety MT-Safe
93 POSIX.1-2001, POSIX.1-2008.
97 returns 1, then the out-of-band data can be read using the
102 Out-of-band data is supported only on some stream socket protocols.
105 can safely be called from a handler for the
110 is implemented using the
119 The following code can be used after receipt of a
121 signal to read (and discard) all data up to the mark,
122 and then read the byte of data at the mark:
130 atmark = sockatmark(sockfd);
132 perror("sockatmark");
139 s = read(sockfd, buf, BUF_LEN);
147 if (recv(sockfd, &oobdata, 1, MSG_OOB) == \-1) {