What Is Value of Eof and '\0' in C

What is value of EOF and '\0' in C

EOF is a macro which expands to an integer constant expression with type int and an implementation dependent negative value but is very commonly -1.

'\0' is a char with value 0 in C++ and an int with the value 0 in C.

The reason why printf("%d",a==EOF); resulted in 1 was because you didn't assign the value EOF to a. Instead you checked if a was equal to EOF and since that was true (a == -1 == EOF) it printed 1.

What is EOF in the C programming language?

On Linux systems and OS X, the character to input to cause an EOF is Ctrl-D. For Windows, it's Ctrl-Z.

Depending on the operating system, this character will only work if it's the first character on a line, i.e. the first character after an Enter. Since console input is often line-oriented, the system may also not recognize the EOF character until after you've followed it up with an Enter.

And yes, if that character is recognized as an EOF, then your program will never see the actual character. Instead, a C program will get a -1 from getchar().

End of File (EOF) in C

EOF indicates "end of file". A newline (which is what happens when you press enter) isn't the end of a file, it's the end of a line, so a newline doesn't terminate this loop.

The code isn't wrong[*], it just doesn't do what you seem to expect. It reads to the end of the input, but you seem to want to read only to the end of a line.

The value of EOF is -1 because it has to be different from any return value from getchar that is an actual character. So getchar returns any character value as an unsigned char, converted to int, which will therefore be non-negative.

If you're typing at the terminal and you want to provoke an end-of-file, use CTRL-D (unix-style systems) or CTRL-Z (Windows). Then after all the input has been read, getchar() will return EOF, and hence getchar() != EOF will be false, and the loop will terminate.

[*] well, it has undefined behavior if the input is more than LONG_MAX characters due to integer overflow, but we can probably forgive that in a simple example.

Representing EOF in C code?

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.

c = getchar() != EOF; prints 0 or 1

Your problem is that a '\n' character is not equal to EOF. The '\n' is being read in as a second character.

Can EOF be on the same line as \n

Can EOF be on the same line as \n

Yes, but rarely.

EOF is a constant usually used to signal 1) end-of-file or a 2) rare input error. It is not usually encoded as a character in a text stream.

A return value of EOF from fgetc() and friends can occur at any time - even in the middle of a line due to an error.

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Otherwise, no:

A end-of-file does not occur at the end of a line with a '\n'. Typically the last line in a file that contains at least 1 character (and no `'\n') will also be a line.

A text stream is an ordered sequence of characters composed into lines, each line consisting of zero or more characters plus a terminating new-line character. Whether the last line requires a terminating new-line character is implementation-defined. C11dr §7.21.2 2

unable to read the EOF character in C

EOF is an integer value outside the range of a char (since its very purpose is to indicate that no char is present), so if you want to be able to compare a value to EOF, then you need to retrieve and store that value as an int rather than as a char.

Why is it needed to give getchar() value of an integer variable in order to have putchar() print all characters?

When you write

while (getchar() != EOF)
    putchar(getchar());

It always

1. reads one character and checks it for EOF,
2. reads one (another) character and prints it,
3. repeats.

Therefore, in your "okok" example, the odd 'o' characters are read, compared to EOF and discarded, and only the even 'k's make it through.

If you wanted to print all of the input characters, you would have to restructure your code. For example, to call getchar() once, save the return value to a variable, then use the already read value twice - check it for EOF and print it.

while (1) {  /* loop forever (until break is called) */
    int ch = getchar();
    if (ch == EOF)
        break;
    putchar(ch);
}

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