Library functions

This section describes the implementation-defined characteristics of the compiler library functions. It corresponds to section ``F.3.14 Library Functions'' in the ANSI document.

Expanding the NULL macro

The macro NULL expands to the null pointer constant:

   0

Diagnostic printed by the assert function

The assert function prints the diagnostic

   "Assertion failed: <expression>, <filename>, <line number>"

   Assertion failed: <comparison operation>, file <source filename>, line <source line number>.

Character testing

The sets of characters that the isalnum, isalpha, iscntrl, islower, isprint, and isupper functions test for are listed below in the section ``Locale-Specific Behavior''.

Math functions and domain errors

Domain errors occur when an input argument is outside the domain over which the mathematical function is defined. When inputs are NaNs or infinities, all the mathematical functions may return various forms of NaNs. When inputs are not NaNs or infinities the values returned by the mathematics functions on the occurrence of domain errors are as presented in the following table:

Math functions and domain errors

Function	Returns
pow()	-HUGE_VAL or -HUGE or 0.0 depending on input values.
sqrt()	0.0
asin()	0.0
acos()	0.0
fmod()	0.0
atan2()	0.0
The value of EDOM is ``33''.

Underflow of floating-point values

On underflow range errors, the mathematics functions listed below set the integer expression errno to the value of the macro ERANGE:

The mathematics functions listed below will get range errors and set the integer expression errno to the value of the macro ERANGE only if the input argument is (±).

Domain errors and the fmod function

The fmod function computes the floating point remainder of x/y. A domain error occurs and zero is returned when the fmod function has a second argument of zero (errno=EDOM).

The signal function

The set of signals for the signal function are:

signal function messages

Signal	Number	Function
SIGHUP	1	hangup
SIGINT	2	interrupt (rubout)
SIGQUIT	3	quit (ASCII FS)
SIGILL	4	illegal instruction (not reset when caught)
SIGTRAP	5	trace trap (not reset when caught)
SIGIOT	6	IOT instruction
SIGABRT	6	used by abort, replace SIGIOT in the future
SIGEMT	7	EMT instruction
SIGFPE	8	floating point exception
SIGKILL	9	kill (cannot be caught or ignored)
SIGBUS	10	bus error
SIGSEGV	11	segmentation violation
SIGSYS	12	bad argument to system call
SIGPIPE	13	write on a pipe with no one to read it
SIGALRM	14	alarm clock
SIGTERM	15	software termination signal from kill
SIGUSR1	16	user defined signal 1
SIGUSR2	17	user defined signal 2
SIGCLD	18	death of a child
SIGCHLD	18	death of a child
SIGPWR	19	power-fail restart
SIGWINCH	20	window change
SIGPOLL	22	pollable event occurred
SIGSTOP	23	sendable stop signal not from tty
SIGTSTP	24	stop signal from tty
SIGCONT	25	continue a stopped process
SIGTTIN	26	to readers pgrp upon background tty read
SIGTTOU	27	like TTIN for output if tp->t_local&TOSTOP
SIGVTALRM	28	virtual timer alarm
SIGPROF	29	profile alarm
SIGXCPU	30	CPU time limit exceeded
SIGXFSZ	31	File size limit exceeded

Default signals

The default handling for each signal recognized by the signal function is to not ignore these signals.

A program runs in a process which inherits its handling of signals from its parent process (such as the shell). If signals are set to SIG_IGN in the parent process, that remains the same. If the signals were set to be caught in the parent they are reset to SIG_DFL which may be to ignore the signal or terminate the program. The setting of SIG_DFL remains the same.

Signal blocking

If the equivalent of "signal(sig, SIG_DFL);" is not executed prior to the call of a signal handler, signal blocking is performed. Signals are set to their default values just before program execution.

The SIGILL signal

The default is not reset if the SIGILL signal is received by a handler specified to the signal function.

Terminating new-line characters

A text stream is an ordered sequence of characters composed into lines, each line consisting of zero of more characters plus a new-line character. The last line of a text stream does not require a terminating new-line character.

Space characters before a new-line character

Space characters written out to a text stream immediately before a new-line character appear when read in.

Null characters appended to a binary stream

A binary stream is an ordered sequence of characters that can transparently record internal data. An unlimited number of null characters may be appended to data written to a binary stream.

File position in append mode

The file position indicator of an append mode stream is initially positioned at the end of the file.

File buffering

Files are fully buffered or unbuffered depending on the setting of setbuf() and setvbuf(). The default buffer size is set by BUFSIZ in stdio.h.

The existence of zero-length files

A zero-length file, one on which no characters have been written by an output stream, actually exists.

Composing valid filenames

The rules for composing valid filenames are:

• The maximum filename length is 14 characters under SCO release 3.2.2.

• The maximum filename length is 255 characters under SCO release 3.2.4.

• The maximum filename length is at least 255 characters and can vary upwards with the type of file system under this release.

• All ASCII characters are acceptable with the exception of ``/''.

• File names ``.'' and ``..'' are not acceptable.

File access limits

The same file can be simultaneously open multiple times.

Removing open files

The effect of the remove function on an open file is to make the file inaccessible to other programs or to users. The file remains accessible to the program, and other running programs that have already opened the file, through already open file descriptors, but not through new attempts to open a file with the same name. Once all open file descriptors are closed, the file will be irrevocably gone unless versioning is enabled.

Renaming with a name that exists

If a file with the new name exists prior to a call to the rename function, rename will succeed, overwriting the existing file in the process.

Output of pointer values

The output for %p conversion in the fprintf function is a hex number. The value may be preceded by a ``0x'' prefix if %#p is used.

Input of pointer values

The input for %p conversion in the fscanf function is a number of hex digits interpreted as a pointer. If %#p is used, ``0x'' is used as a prefix. This option is identical to the %x conversion specifier.

Reading ranges

A ``-'' character that is neither the first nor the last character in the scanlist for %[ conversion in the fscanf function is interpreted as a range indicator as long as the character to the left is less than the character to the right of the ``-''. The following example selects all upper-case ASCII characters from ``A'' to ``Z'' inclusive:

   %[A-Z]

File position errors

The errno is set to EBADF or ESPIPE by the fgetpos or ftell function on failure. EINVAL may be generated by the lseek() system call (ftell() and fgetpos() call lseek()).

Messages generated by the perror function

The messages generated by the perror function look like:

   <some user message>: <error message>

Allocating zero memory

The calloc, malloc and realloc functions return a pointer to a zero-sized block if the size requested is zero. For calloc and malloc this is different behavior from the behavior of the functions in libmalloc.a which return a NULL on malloc(0).

The abort function and open and temporary files

When the abort function is executed, the buffers of open and temporary files are flushed, all files are closed, and execution returns to the shell.

The exit function

The exit() function returns the lower byte of its argument to the shell if the value of the argument is other than zero, EXIT_SUCCESS, or EXIT_FAILURE. The shell or the user may interpret this value in any way. Unsuccessful termination is indicated by a return of non-zero. Successful termination is indicated by a return value of zero.

Environment names

The set of environment names is that set exported by the parent process.

The system function

Any UNIX command line that is acceptable to the Bourne Shell can be passed as the string to the system function. The Bourne Shell is assumed to be the command processor and that shell is run as a child process to the program's (that is, parent) process.

The strerror function

The strerror function generates the following messages:

strerror function messages

Number	Message	Error
1	Operation not permitted	EPERM
2	No such file or directory	ENOENT
3	No such process	ESRCH
4	Interrupted system call	EINTR
5	I/O error	EIO
6	No such device or address	ENXIO
7	Arg list too long	E2BIG
8	Exec format error	ENOEXEC
9	Bad file number	EBADF
10	No child processes	ECHILD
11	Resource temporarily unavailable	EAGAIN
12	Not enough space	ENOMEM
13	Permission denied	EACCES
14	Bad address	EFAULT
15	Block device required	ENOTBLK
16	Device busy	EBUSY
17	File exists	EEXIST
18	Cross-device link	EXDEV
19	No such device	ENODEV
20	Not a directory	ENOTDIR
21	Is a directory	EISDIR
22	Invalid argument	EINVAL
23	File table overflow	ENFILE
24	Too many open files	EMFILE
25	Inappropriate I/O control operation	ENOTTY
26	Text file busy	ETXTBSY
27	File too large	EFBIG
28	No space left on device	ENOSPC
29	Illegal seek	ESPIPE
30	Read-only file system	EROFS
31	Too many links	EMLINK
32	Broken pipe	EPIPE
33	Argument out of domain	EDOM
34	Result too large or too small	ERANGE
35	No message of desired type	ENOMSG
36	Identifier removed	EIDRM
37	Channel number out of range	ECHRNG
38	Level 2 not synchronized	EL2NSYNC
39	Level 3 halted	EL3HLT
40	Level 3 reset	EL3RST
41	Link number out of range	ELNRNG
42	Protocol driver not attached	EUNATCH
43	No CSI structure available	ENOCSI
44	Level 2 halted	EL2HLT
45	Deadlock situation detected/avoided	EDEADLK
46	No record locks available	ENOLCK
50	Bad exchange descriptor	EBADE
51	Bad request descriptor	EBADR
52	Message tables full	EXFULL
53	Anode table overflow	ENOANO
54	Bad request code	EBADRQC
55	Invalid slot	EBADSLT
56	File locking deadlock	EDEADLOCK
57	Bad font file format	EBFONT
60	Not a stream device	ENOSTR
61	No data available	ENODATA
62	Timer expired	ETIME
63	Out of stream resources	ENOSR
64	Machine is not on the network	ENONET
65	Package not installed	ENOPKG
66	Object is remote	EREMOTE
67	Link has been severed	ENOLINK
68	Advertise error	EADV
69	Srmount error	ESRMNT
70	Communication error on send	ECOMM
71	Protocol error	EPROTO
74	Multihop attempted	EMULTIHOP
75	Inode is remote	ELBIN
76	Cross mount point	EDOTDOT
77	Not a data message	EBADMSG
78	Filename too long	ENAMETOOLONG
79	Value too large for defined data type	EOVERFLOW
80	Name not unique on network	ENOTUNIQ
81	File descriptor in bad state	EBADFD
82	Remote address changed	EREMCHG
83	Can not access a needed shared library	ELIBACC
84	Accessing a corrupted shared library	ELIBBAD
85	.lib section in a.out corrupted	ELIBSCN
86	Attempting to link in more shared libraries than system limit	ELIBMAX
87	Can not exec a shared library directly	ELIBEXEC
88	Illegal byte sequence	EILSEQ
89	Function not implemented	ENOSYS
90	Operation would block	_TCPERR
91	Operation now in progress	EINPROGRESS
92	Operation already in progress	EALREADY
93	Socket operation on non-socket	ENOTSOCK
94	Destination address required	EDESTADDRREQ
95	Message too long	EMSGSIZE
96	Protocol wrong type for socket	EPROTOTYPE
97	Protocol not supported	EPROTONOSUPPORT
98	Socket type not supported	ESOCKTNOSUPPORT
99	Operation not supported on socket	EOPNOTSUPP
100	Protocol family not supported	EPFNOSUPPORT
101	Address family not supported by protocol family	EAFNOSUPPORT
102	Address already in use	EADDRINUSE
103	Cannot assign requested address	EADDRNOTAVAIL
104	Network is down	ENETDOWN
105	Network is unreachable	ENETUNREACH
106	Network dropped connection on reset	ENETRESET
107	Software caused connection abort	ECONNABORTED
108	Connection reset by peer	ECONNRESET
110	Socket is already connected	EISCONN
111	Socket is not connected	ENOTCONN
112	Cannot send after socket shutdown	ESHUTDOWN
113	Too many references: cannot splice	ETOOMANYREFS
114	Connection timed out	ETIMEDOUT
115	Connection refused	ECONNREFUSED
116	Host is down	EHOSTDOWN
117	No route to host	EHOSTUNREACH
118	Protocol not available	ENOPROTOOPT
135	Structure needs cleaning	EUCLEAN
137	Not a name file	ENOTNAM
138	Not available	ENAVAIL
139	Is a name file	EISNAM
140	Remote I/O error	EREMOTEIO
141	Reserved for future use	EINIT
142	Unknown error: 142	EREMDEV
145	Directory not empty	ENOTEMPTY
150	Too many symbolic links in path	ELOOP
151	Stale NFS file handle	ESTALE
152	Restartable system call	ERESTART
153	No sleeping in stream head of pipe/FIFO	ESTRPIPE
500	Unknown error	EIORESID

The time zone

The local time zone (with or without daylight savings) is read from an environment variable called TZ at program runtime. That variable assists in interpreting the system clock. If no such environment variable is set the default is to GMT (non-daylight savings time).

The clock function

The era for the clock function is: January 1 1970 00:00 GMT.