Why output close

So when we called second open , then first unused fd is also 3. So, output of this program is 3. A successful read updates the access time for the file. Also, some times read system call should read less bytes than cnt. Those bytes are as follows: 0 0 0 foo. Suppose that foobar. Then what is the output of the following program? Thus, the read from fd2 reads the first byte of foobar.

If cnt is zero, write simply returns 0 without attempting any other action. This happens when fd have a less number of bytes to write than cnt. If write is interrupted by a signal, the effect is one of the following: -If write has not written any data yet, it returns -1 and sets errno to EINTR. If foo. WriteLine methods are equivalent to calls to the corresponding WriteLine methods.

Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. Skip to main content. This browser is no longer supported.

InputTextString string returns an input stream that delivers the characters from the string string. The string is not changed when reading characters from it and changing the string after the call to InputTextString has no influence on the input stream. If append is false , then the list is emptied first, otherwise received characters are added at the end of the list. Input-output streams capture bidirectional communications between GAP and another process, either locally or as yet unimplemented remotely.

Such streams support the basic operations of both input and output streams. They should provide some buffering, allowing output data to be written to the stream, even when input data is waiting to be read, but the amount of this buffering is operating system dependent, and the user should take care not to get too far ahead in writing, or behind in reading, or deadlock may occur. At present the only type of Input-Output streams that are implemented provide communication with a local child process, using a pseudo-tty.

Like other streams, write operations are blocking, read operations will block to get the first character, but not thereafter. As far as possible, no translation is done on characters written to, or read from the stream, and no control characters have special effects, but the details of particular pseudo-tty implementations may effect this. Bytes written to this stream are received by the slave process as if typed at a terminal on standard input.

Bytes written to standard output by the slave process can be read from the stream. If the argument nofail which must be false or true is provided and it is set to true then ReadAllLine will wait, if necessary, for input and never return fail.

If the argument IsAllLine which must be a function that takes a string argument and returns either true or false then it is used to determine what constitutes a whole line. The default behaviour is equivalent to passing the function. The purpose of the IsAllLine argument is to cater for the case where the input being read is from an external process that writes a "prompt" for data that does not terminate with a newline.

The following two commands create dummy streams which will consume all characters and never deliver one. Its main use is for calls to Process This section describes a feature of the GAP kernel that can be used to handle pending streams somehow "in the background".

This is only available on operating systems that have select. Right before GAP reads a keypress from the keyboard it calls a little subroutine that can handle streams that are ready to be read or ready to be written. This means that GAP can handle these streams during user input on the command line. Note that this does not work when GAP is in the middle of some calculation. This feature is used in the following way.

Note that handler functions must not return anything and get one integer argument, which refers to an index in one of the following arrays according to whether the function was installed for input, output or exceptions on the stream.

Handler functions usually should not output anything on the standard output because this ruins the command line during command line editing. The argument mode decides, for what operations on the stream this function is installed. More than one letter is allowed in mode. As described above the function is called in a situation when GAP is reading a character from the keyboard. Handler functions should not use much time to complete.

This functionality only works if the operating system has a select function. All instances are deinstalled, regardless of the mode of operation read, write, exception. In some situations it can be desirable to process data given in the form of a spreadsheet such as Excel.

GAP can do this using the CSV comma separated values format, which spreadsheet programs can usually read in or write out. The first line of the spreadsheet is used as labels of record components, each subsequent line then corresponds to a record.

Entries enclosed in double quotes are considered as strings and are permitted to contain the separation character usually a comma. This function reads in a spreadsheet, saved in CSV format c omma s eparated v alues and returns its entries as a list of records. The entries of the first line of the spreadsheet are used to denote the names of the record components. Blanks will be translated into underscore characters.

If the parameter nohead is given as true , instead the record components will be called fieldn. Case does not matter. As this is an advanced feature, discussion is delayed until Two-Way Communications with Another Process , which describes it in more detail and gives an example. In many older versions of Unix awk , the close function is actually a statement.

It is a syntax error to try and use the return value from close :. The return value is -1 if the argument names something that was never opened with a redirection, or if there is a system problem closing the file or process. In gawk , starting with version 4. This value is zero if the close succeeds, or -1 if it fails. The POSIX standard is very vague; it says that close returns zero on success and a nonzero value otherwise.

In general, different implementations vary in what they report when closing pipes; thus, the return value cannot be used portably. The technical terminology is rather morbid.