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25 .TH SOCKATMARK 3 2017-09-15 "Linux" "Linux Programmer's Manual"
27 sockatmark \- determine whether socket is at out-of-band mark
29 .B #include <sys/socket.h>
31 .BI "int sockatmark(int " sockfd );
34 Feature Test Macro Requirements for glibc (see
35 .BR feature_test_macros (7)):
40 _POSIX_C_SOURCE\ >=\ 200112L
44 returns a value indicating whether or not the socket referred
45 to by the file descriptor
47 is at the out-of-band mark.
48 If the socket is at the mark, then 1 is returned;
49 if the socket is not at the mark, 0 is returned.
50 This function does not remove the out-of-band mark.
54 returns 1 if the socket is at the out-of-band mark, or 0 if it is not.
55 On error, \-1 is returned and
57 is set to indicate the error.
62 is not a valid file descriptor.
65 .\" POSIX.1 says ENOTTY for this case
67 is not a file descriptor to which
72 was added to glibc in version 2.2.4.
74 For an explanation of the terms used in this section, see
80 Interface Attribute Value
83 T} Thread safety MT-Safe
86 POSIX.1-2001, POSIX.1-2008.
90 returns 1, then the out-of-band data can be read using the
95 Out-of-band data is supported only on some stream socket protocols.
98 can safely be called from a handler for the
103 is implemented using the
112 The following code can be used after receipt of a
114 signal to read (and discard) all data up to the mark,
115 and then read the byte of data at the mark:
123 atmark = sockatmark(sockfd);
125 perror("sockatmark");
132 s = read(sockfd, buf, BUF_LEN);
140 if (recv(sockfd, &oobdata, 1, MSG_OOB) == \-1) {