Error code set by system functions
Int_Type errno
A system function can fail for a variety of reasons. For example, a
file operation may fail because lack of disk space, or the process
does not have permission to perform the operation. Such functions
will return -1 and set the variable errno to an error
code describing the reason for failure.
Particular values of errno may be specified by the following
symbolic constants (read-only variables) and the corresponding
errno_string value:
EPERM "Not owner"
ENOENT "No such file or directory"
ESRCH "No such process"
ENXIO "No such device or address"
ENOEXEC "Exec format error"
EBADF "Bad file number"
ECHILD "No children"
ENOMEM "Not enough core"
EACCES "Permission denied"
EFAULT "Bad address"
ENOTBLK "Block device required"
EBUSY "Mount device busy"
EEXIST "File exists"
EXDEV "Cross-device link"
ENODEV "No such device"
ENOTDIR "Not a directory"
EISDIR "Is a directory"
EINVAL "Invalid argument"
ENFILE "File table overflow"
EMFILE "Too many open files"
ENOTTY "Not a typewriter"
ETXTBSY "Text file busy"
EFBIG "File too large"
ENOSPC "No space left on device"
ESPIPE "Illegal seek"
EROFS "Read-only file system"
EMLINK "Too many links"
EPIPE "Broken pipe"
ELOOP "Too many levels of symbolic links"
ENAMETOOLONG "File name too long"
The mkdir function will attempt to create a directory. If
that directory already exists, the function will fail and set
errno to EEXIST.
define create_dir (dir)
{
if (0 == mkdir (dir)) return;
if (errno != EEXIST)
throw IOError, sprintf ("mkdir %s failed: %s",
dir, errno_string (errno));
}
errno_string, error, mkdir
Return a string describing an errno.
String_Type errno_string ( [Int_Type err ])
The errno_string function returns a string describing the
integer errno code err. If the err parameter is
omitted, the current value of errno will be used. See the
description for errno for more information.
The errno_string function may be used as follows:
define sizeof_file (file)
{
variable st = stat_file (file);
if (st == NULL)
throw IOError, sprintf ("%s: %s", file, errno_string (errno));
return st.st_size;
}
errno, stat_file
Generate an error condition (deprecated)
error (String_Type msg
This function has been deprecated in favor of throw.
The error function generates a S-Lang RunTimeError
exception. It takes a single string parameter which is displayed on
the stderr output device.
define add_txt_extension (file)
{
if (typeof (file) != String_Type)
error ("add_extension: parameter must be a string");
file += ".txt";
return file;
}
verror, message
Print a string onto the message device
message (String_Type s
The message function will print the string specified by
s onto the message device.
define print_current_time ()
{
message (time ());
}
The message device will depend upon the application. For example, the output message device for the jed editor corresponds to the line at the bottom of the display window. The default message device is the standard output device.
vmessage, sprintf, error
Create a new exception
new_exception (String_Type name, Int_Type baseclass, String_Type descr)
This function creates a new exception called name subclassed
upon baseclass. The description of the exception is
specified by descr.
new_exception ("MyError", RunTimeError, "My very own error");
try
{
if (something_is_wrong ())
throw MyError;
}
catch RunTimeError;
RunTimeError will also catch
MyError since it is a subclass of RunTimeError.
error, verror
Generate a usage error
usage (String_Type msg)
The usage function generates a UsageError exception and
displays msg to the message device.
Suppose that a function called plot plots an array of x and
y values. Then such a function could be written to issue a
usage message if the wrong number of arguments was passed:
define plot ()
{
variable x, y;
if (_NARGS != 2)
usage ("plot (x, y)");
(x, y) = ();
% Now do the hard part
.
.
}
error, message
Generate an error condition (deprecated)
verror (String_Type fmt, ...)
This function has been deprecated in favor or throw.
The verror function performs the same role as the error
function. The only difference is that instead of a single string
argument, verror takes a sprintf style argument list.
define open_file (file)
{
variable fp;
fp = fopen (file, "r");
if (fp == NULL) verror ("Unable to open %s", file);
return fp;
}
In the current implementation, the verror function is not an
intrinsic function. Rather it is a predefined S-Lang function using
a combination of sprintf and error.
To generate a specific exception, a throw statement should be
used. In fact, a throw statement such as:
if (fp == NULL)
throw OpenError, "Unable to open $file"$;
verror in the above example.
error, Sprintf, vmessage
Print a formatted string onto the message device
vmessage (String_Type fmt, ...)
The vmessage function formats a sprintf style argument list
and displays the resulting string onto the message device.
In the current implementation, the vmessage function is not an
intrinsic function. Rather it is a predefined S-Lang function using
a combination of Sprintf and message.
message, sprintf, Sprintf, verror