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read will eventually run out of characters to read from the file, potentially on its very first call, which would leave a in an undetermined state and potentially cause write to cause a null pointer exception. To avoid this, read returns the special value EOF (end-of-file) in this situation, which requires an explicit test to avoid writeing it:
In 1973, ECMA-35 and ISO 2022 [18] attempted to define a method so an 8-bit "extended ASCII" code could be converted to a corresponding 7-bit code, and vice versa. [19] In a 7-bit environment, the Shift Out would change the meaning of the 96 bytes 0x20 through 0x7F [a] [21] (i.e. all but the C0 control codes), to be the characters that an 8-bit environment would print if it used the same code ...
In the C standard library, the character-reading functions such as getchar return a value equal to the symbolic value (macro) EOF to indicate that an end-of-file condition has occurred. The actual value of EOF is implementation-dependent and must be negative (it is commonly −1, such as in glibc [2]).
here doc with <<-a single space character (i.e. 0x20 ) is at the beginning of this line this line begins with a single tab character i.e 0x09 as does the next line the intended end was before this line and these were not processed by tr +++++ here doc with << a single space character (i.e. 0x20 ) is at the beginning of this line this line ...
The DOS Control-Z byte is actually sent and/or placed in files to indicate where the text ends. In contrast, the Control-D causes the Unix terminal driver to signal the EOF condition, which is not a character, while the byte has no special meaning if actually read or written from a file or terminal.
function LookupCode (sCode as string) as integer dim iReturnValue as integer dim sLine, sPath as string sPath = "C:\Test.dsv" if FileExists (sPath) then open sPath for input as # 1 do while not EOF (1) line input # 1, sLine if sCode = left (sLine, 3) then 'Action(s) to be carried out End if loop close # 1 End if LookupCode = iReturnValue end function
A common use might be to control access to a data structure in memory that cannot be updated atomically and is invalid (and should not be read by another thread) until the update is complete. Readers–writer locks are usually constructed on top of mutexes and condition variables , or on top of semaphores .
More generally, Python 2.x specifies the built-in file objects as being “implemented using C's stdio package," [48] and frequent reference is made to C standard library behaviors; the available operations (open, read, write, etc.) are expected to have the same behavior as the corresponding C functions (fopen, fread, fwrite, etc.).