Representing EOF in C code

Question

The newline character is represented by   n  in C code  Is there an equivalent for the end-of-file  EOF  character

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There is the constant EOF of type int  found in stdio h  There is no equivalent character literal specified by any standard

User · Answer

This is system dependent but often -1  See here

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The EOF character recognized by the command interpreter on Windows  and MSDOS  and CP M  is 0x1a  decimal 26  aka Ctrl Z aka SUB  It can still be be used today for example to mark the end of a human-readable header in a binary file  if the file begins with  quot Some description x1a quot  the user can dump the file content to the console using the TYPE command and the dump will stop at the EOF character  i e  print Some description and stop  instead of continuing with the garbage that follows

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I think it may vary from system to system but one way of checking would be to just use printf   include  lt stdio h gt  int main void        printf   d   EOF       return 0      I did this on Windows and -1 was printed to the console  Hope this helps

User · Answer

The value of EOF can t be confused with any real character   If a  getchar    then we must declare a big enough to hold any value that getchar   returns  We can t use char since a must be big enough to hold EOF in addition to characters

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EOF is not a character  in most modern operating systems   It is simply a condition that applies to a file stream when the end of the stream is reached  The confusion arises because a user may signal EOF for console input by typing a special character  e g Control-D in Unix  Linux  et al   but this character is not seen by the running program  it is caught by the operating system which in turn signals EOF to the process   Note  in some very old operating systems EOF was a character  e g  Control-Z in CP M  but this was a crude hack to avoid the overhead of maintaining actual file lengths in file system directories

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I have been researching a lot about the EOF signal  In the book on Programming in C by Dennis Ritchie it is first encountered while introducing putchar   and getchar   commands  It basically marks the end of the character string input  For eg  Let us write a program that seeks two numerical inputs and prints their sum  You ll notice after each numerical input you press Enter to mark the signal that you have completed the iput action  But while working with character strings Enter is read as just another character    n   newline character   To mark the termination of input you enter  Z Ctrl   Z on keyboard  in a completely new line and then enter  That signals the next lines of command to get executed   include  lt stdio h gt   int main     char c  int i   0  printf  quot INPUT  t quot    c   getchar     while  c    EOF         i     c   getchar            printf  quot NUMBER OF CHARACTERS  d  quot   i    return 0    The above is the code to count number of characters including   n  newline  and   t   space  characters  If you don t wanna count the newline characters do this    include  lt stdio h gt   int main     char c  int i   0  printf  quot INPUT  t quot    c   getchar     while  c    EOF        if  c      n                   i             c   getchar            printf  quot NUMBER OF CHARACTERS  d  quot   i    return 0      NOW THE MAIN THINK HOOW TO GIVE INPUT  IT S SIMPLE  Write all the story you want then go in a new line and enter  Z and then enter again

User · Answer

No  EOF is not a character  but a state of the filehandle   While there are there are control characters in the ASCII charset that represents the end of the data  these are not used to signal the end of files in general  For example EOT   D  which in some cases almost signals the same   When the standard C library uses signed integer to return characters and uses -1 for end of file  this is actually just the signal to indicate than an error happened  I don t have the C standard available  but to quote SUSv3      If the end-of-file indicator for the stream is set  or if the stream is at end-of-file  the end-of-file indicator for the stream shall be set and fgetc   shall return EOF  If a read error occurs  the error indicator for the stream shall be set  fgetc   shall return EOF  and shall set errno to indicate the error

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EOF is not a character  It can t be  A  binary  file can contain any character  Assume you have a file with ever-increasing bytes  going 0 1 2 3     255 and once again 0 1     255  for a total of 512 bytes  Whichever one of those 256 possible bytes you deem EOF  the file will be cut short   That s why getchar   et al  return an int  The range of possible return values are those that a char can have  plus a genuine int value EOF  defined in stdio h   That s also why converting the return value to a char before checking for EOF will not work   Note that some protocols have  EOF   characters   ASCII has  End of Text    End of Transmission    End of Transmission Block  and  End of Medium   Other answers have mentioned old OS es  I myself input  D on Linux and  Z on Windows consoles to stop giving programs input   But files read via pipes can have  D and  Z characters anywhere and only signal EOF when they run out of bytes   C strings are terminated with the   0  character  but that also means they cannot contain the character   0   That s why all C non-string data functions work using a char array  to contain the data  and a size t  to know where the data ends    Edit  The C99 standard   7 19 1 3 states      The macros are         EOF   which expands to an integer constant expression  with type int and a negative value  that is returned by several functions to   indicate end-of- le  that is  no more input from a stream

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I ve read all the comments  It s interesting to notice what happens when you print out this   printf   nInteger       d n   EOF                 OUTPUT   -1 printf  Decimal       d n   EOF                   OUTPUT   -1 printf  Octal     o n   EOF                       OUTPUT   37777777777 printf  Hexadecimal     x n   EOF                 OUTPUT   ffffffff printf  Double and float     f n   EOF            OUTPUT   0 000000 printf  Long double     Lf n   EOF                OUTPUT   0 000000 printf  Character     c n   EOF                   OUTPUT   nothing   As we can see here  EOF is NOT a character  whatsoever

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The answer is NO  but     You may confused because of the behavior of fgets    From http   www cplusplus com reference cstdio fgets        Reads characters from stream and stores them as a C string into str until  num-1  characters have been read or either a newline or the end-of-file is reached  whichever happens first

[c] Representing EOF in C code?

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