How do you get to see the last print? In other words what to put in for EOF? I checked the definitions and it says EOF is -1.
And if you enter Ctrl-D you won't see anything.
#include <stdio.h>
int main() {
int c;
while((c = getchar() != EOF)) {
printf("%d\n", c);
}
printf("%d - at EOF\n", c);
}
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().
You should change your parenthesis to
while((c = getchar()) != EOF)
Because the "=" operator has a lower precedence than the "!=" operator. Then you will get the expected results. Your expression is equal to
while (c = (getchar()!= EOF))
You are getting the two 1's as output, because you are making the comparison "c!=EOF". This will always become one for the character you entered and then the "\n" that follows by hitting return. Except for the last comparison where c really is EOF it will give you a 0.
EDIT about EOF: EOF is typically -1, but this is not guaranteed by the standard. The standard only defines about EOF in section 7.19.1:
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-file, that is, no more input
from a stream;
It is reasonable to assume that EOF equals -1, but when using EOF you should not test against the specific value, but rather use the macro.
The value of EOF is a negative integer to distinguish it from "char" values that are in the range 0 to 255. It is typically -1, but it could be any other negative number ... according to the POSIX specs, so you should not assume it is -1.
The ^D character is what you type at a console stream on UNIX/Linux to tell it to logically end an input stream. But in other contexts (like when you are reading from a file) it is just another data character. Either way, the ^D character (meaning end of input) never makes it to application code.
As #Bastien says, EOF is also returned if getchar() fails. Strictly speaking, you should call ferror or feof to see whether the EOF represents an error or an end of stream. But in most cases your application will do the same thing in either case.
Couple of typos:
while((c = getchar())!= EOF)
in place of:
while((c = getchar() != EOF))
Also getchar() treats a return key as a valid input, so you need to buffer it too.EOF is a marker to indicate end of input. Generally it is an int with all bits set.
#include <stdio.h>
int main()
{
int c;
while((c = getchar())!= EOF)
{
if( getchar() == EOF )
break;
printf(" %d\n", c);
}
printf("%d %u %x- at EOF\n", c , c, c);
}
prints:
49
50
-1 4294967295 ffffffff- at EOF
for input:
1
2
<ctrl-d>
EOF means end of file. It's a sign that the end of a file is reached, and that there will be no data anymore.
Edit:
I stand corrected. In this case it's not an end of file. As mentioned, it is passed when CTRL+d (linux) or CTRL+z (windows) is passed.
nput from a terminal never really "ends" (unless the device is disconnected), but it is useful to enter more than one "file" into a terminal, so a key sequence is reserved to indicate end of input. In UNIX the translation of the keystroke to EOF is performed by the terminal driver, so a program does not need to distinguish terminals from other input files. By default, the driver converts a Control-D character at the start of a line into an end-of-file indicator. To insert an actual Control-D (ASCII 04) character into the input stream, the user precedes it with a "quote" command character (usually Control-V). AmigaDOS is similar but uses Control-\ instead of Control-D.
In Microsoft's DOS and Windows (and in CP/M and many DEC operating systems), reading from the terminal will never produce an EOF. Instead, programs recognize that the source is a terminal (or other "character device") and interpret a given reserved character or sequence as an end-of-file indicator; most commonly this is an ASCII Control-Z, code 26. Some MS-DOS programs, including parts of the Microsoft MS-DOS shell (COMMAND.COM) and operating-system utility programs (such as EDLIN), treat a Control-Z in a text file as marking the end of meaningful data, and/or append a Control-Z to the end when writing a text file. This was done for two reasons:
Backward compatibility with CP/M. The CP/M file system only recorded the lengths of files in multiples of 128-byte "records", so by convention a Control-Z character was used to mark the end of meaningful data if it ended in the middle of a record. The MS-DOS filesystem has always recorded the exact byte-length of files, so this was never necessary on MS-DOS.
It allows programs to use the same code to read input from both a terminal and a text file.
#include <stdio.h>
int main() {
int c;
while((c = getchar()) != EOF) { //precedence of != is greater than =, so use braces
printf("%d\n", c);
}
printf("%d - at EOF\n", c);
}
I think this is right way to check value of EOF.
And I checked the output.
For INPUT: abc and Enter I got OUTPUT: 97 98 99 10. ( the ASCII values)
For INPUT Ctrl-D I got OUTPUT: -1 - at EOF.
So I think -1 is the value for EOF.
Try other inputs instead of Ctrl-D, like Ctrl-Z.
I think it varies from compiler to compiler.
to keep it simple: EOF is an integer type with value -1. Therefore, we must use an integer variable to test EOF.
#include <stdio.h>
int main() {
int c;
while((c = getchar()) != EOF) {
putchar(c);
}
printf("%d at EOF\n", c);
}
modified the above code to give more clarity on EOF, Press Ctrl+d and putchar is used to print the char avoid using printf within while loop.
int c;
while((c = getchar())!= 10)
{
if( getchar() == EOF )
break;
printf(" %d\n", c);
}
Related
When I run the following code and input a sentence I am not given any output. The cursor just goes to a new line.
I copied this straight off the book and double checked it for mistakes (1st edition C programming language by kernighan & ritchie)
#include <stdio.h>
int main()
{
int c,i,nwhite,nother;
int ndigit[10];
nwhite=nother=0;
for(i=0;i<10;++i)
ndigit[i] = 0;
while (( c=getchar()) != EOF)
if(c>= '0' && c<= '9')
++ndigit[c-'0'];
else if (c==' ' || c == '\n' || c == '\t')
++nwhite;
else
++nother;
printf("digits =");
for( i=0; i<10; ++i)
printf("%d",ndigit[i]);
printf(", white space = %d, other = %d\n", nwhite,nother);
return 0;
}
Since you are testing a program copied from another source, I suppose that you don't want to change it, but understanding it.
getchar() obtains exactly 1 character from the standard input, which is a file named stdin in the standard header <stdio.h>.
The standard input, stdin, is considered a file.
Formally speaking, the end-of-file is a "mark" and not a "character".
However, in general, a specific "character" is used to mark the "end-of-file" of a text file.
In Windows the "end-of-file" mark is the character CTRL-Z (whose ASCII code is 26).
In Linxu the mark is CTRL-D (whose ASCII code is 4).
On the other hand, the standard input commonly has the following behaviour:
Wait for user enter characters until an Intro/Enter key is pressed.
If the user does not press Enter, then the standard input does not give back the control to the program. This happens even if you enter an "end-of-file" character (say, CTRL-Z).
However, other behaviours are possible.
For example, in Ubuntu console I obtain that CTRL-D is recognized without waiting for the Enter key be pressed.
In any case, you must explicitely type the end-of-file mark in the console of your system.
So, CTRL-Z (perhaps followed by Enter) or CTRL-D have to be pressed for yourself.
ABOUT ENTER and EOF
After Enter is pressed, your program test for EOF, that is, the "end-of-file" mark in your system.
However, the Enter keyword does not prints "end-of-file" marks, but only "end-of-line" ones, which corresponds to the standard character newline '\n'.
Thus, if it is desired that the while() loop terminates after pressing Intro/Enter, the test must be done against '\n', and not EOF.
AN OBSERVATION
It can be observed that getchar() doesn't retrieve the character CTRL-Z, because the ASCII code for CTRL-Z is 26, but getchar() retrieves a negative value (in general -1).
This means that getchar() recognizes the character ASCII 26 as and end-of-file mark, and then it converts to a value with meaning in C, provided by the macro EOF, which is not 26.
What I mean is that EOF is not CTRL-Z, and then one cannot naively send EOF under the assumption that the ASCII 26 (CTRL-Z) will be sent to a text file.
Summarizing, I think that it is important to delucidate the abstract concept of "end-of-file", the role of EOF, and the difference between a "mark" and a "character".
(Another example: in Windows the "mark" for "end-of-line" is the couple of characters CTRL-M CTRL-J, which is not only 1 character, but 2).
Quoted from the standard:
The getchar function returns the next character from the input stream pointed to by
stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
getchar returns EOF.
*Note: I'm using windows, so EOF is ctrl + Z for me.
For a while I've noticed an EOF input seems to behave differently in isolation than it does when accompanied by other input. For example, ^Z (the EOF command for windows in command prompt) and a^Z seem to cause different behavior in the following code:
#include <stdio.h>
#define MAX 1000
int getline(char s[]);
main() {
int line;
char arr[MAX];
while( (line = getline(arr)) != EOF)
printf("%s",arr);
system("Pause");
return 0;
}
int getline(char s[])
{
int c, i = 0;
while ((c = getchar()) != EOF && c != '\n') {
s[i++] = c;
}
if (c == '\n') {
s[i++] = c;
}
else
return EOF;
s[i] = '\0';
return 1;
}
If I input ^Z + enter in the command prompt, the program predictably jumps to system("Pause"); However, if I input abc^Z + enter, nothing happens, as though EOF was ignored and a '\n' command was never received. If, at this point, I press enter again, it shows the following:
I've been tinkering with and debugging this code and small variations of it for over an hour now and can't seem to find anything wrong with it. In theory, if I input abc^Z + enter, I expect the input to be interpreted as abcEOF\n, which would give:
s[0] = 'a'
s[1] = 'b'
s[2] = 'c'
i = 3 when loop breaks from c = EOF
if (c == '\n') skipped since c = EOF
leads to else -> return EOF
in main(), line = EOF since that is what the function getline returned
while loop breaks because of above
system("Pause"); follows
Is there something wrong with my code that I'm overlooking or is there some quirk to EOF or command prompt that I should be aware of? I'm almost certain this isn't the only instance where mixing ^Z with other values caused unintended behavior.
Don't think of CTRL-Z as the end-of-file character, there is actually a real character with code point 26 (which is what you'd normally expect CTRL-Z to generate).
Instead, think of CTRL-Z as a way for your terminal device to indicate the end of the input stream to your program. If you were to read a real file of the disk and it contained CTRL-Z, it should keep going (though that may not be the case in certain implementations where you, for example, open it with the mode r instead of rb).
In Windows, that translation of CTRL-Z to the end-stream operation only happens when it appears at the start of the line which is why you're not getting EOF when you enter abcCTRL-Z.
When you enter CTRL-Z on a character position that isn't the start of the line, it's treated as a real CTRL-Z, not a stream-closing operation. That's why you're getting that → character, which is the printable character at code point 26.
It is the normal behaviour of getchar..
getchar() is a standard function and requires you to press *ENTER* to get the input
Many compilers/platforms support the non-standard getch() that does not require ENTER.
EOF is not a character. The EOF is a macro that getchar() returns when it reaches the end of input or encounters some kind of error
The newline character is represented by "\n" in C code. Is there an equivalent for the end-of-file (EOF) character?
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.
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-file, that is, no more input from a stream;
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.
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).
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 "Some description\x1a" 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.
This is system dependent but often -1. See here
I think it may vary from system to system but one way of checking would be to just use printf
#include <stdio.h>
int main(void)
{
printf("%d", EOF);
return 0;
}
I did this on Windows and -1 was printed to the console. Hope this helps.
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.
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.
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 <stdio.h>
int main()
{
char c;
int i = 0;
printf("INPUT:\t");
c = getchar();
while (c != EOF)
{
++i;
c = getchar();
};
printf("NUMBER OF CHARACTERS %d.", 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 <stdio.h>
int main()
{
char c;
int i = 0;
printf("INPUT:\t");
c = getchar();
while (c != EOF)
{
if (c != '\n')
{
++i;
}
c = getchar();
};
printf("NUMBER OF CHARACTERS %d.", 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.
There is the constant EOF of type int, found in stdio.h. There is no equivalent character literal specified by any standard.
I'm reading The C Programming Language and have understood everything so far.
However when I came across the getchar() and putchar(), I failed to understand what is their use, and more specifically, what the following code does.
main()
{
int c;
while ((c = getchar()) != EOF)
putchar(c);
}
I understand the main() function, the declaration of the integer c and the while loop. Yet I'm confused about the condition inside of the while loop. What is the input in this C code, and what is the output.
This code can be written more clearly as:
main()
{
int c;
while (1) {
c = getchar(); // Get one character from the input
if (c == EOF) { break; } // Exit the loop if we receive EOF ("end of file")
putchar(c); // Put the character to the output
}
}
The EOF character is received when there is no more input. The name makes more sense in the case where the input is being read from a real file, rather than user input (which is a special case of a file).
[As an aside, generally the main function should be written as int main(void).]
getchar() is a function that reads a character from standard input. EOF is a special character used in C to state that the END OF FILE has been reached.
Usually you will get an EOF character returning from getchar() when your standard input is other than console (i.e., a file).
If you run your program in unix like this:
$ cat somefile | ./your_program
Then your getchar() will return every single character in somefile and EOF as soon as somefile ends.
If you run your program like this:
$ ./your_program
And send a EOF through the console (by hitting CTRL+D in Unix or CTRL+Z in Windows), then getchar() will also returns EOF and the execution will end.
The code written with current C standards should be
#include <stdio.h>
int main(void)
{
int c;
while ((c = getchar()) != EOF)
putchar(c);
}
The loop could be rewritten as
int c;
while (1) {
c = getchar();
if (c != EOF)
putchar(c);
else
break;
}
this reads as
repeat forever
get the next character ("byte") of input from standard input and store it into c
if no exceptional condition occurred while reading the said character
then output the character stored into c into standard output
else
break the loop
Many programming languages handle exceptional conditions through raising exceptions that break the normal program flow. C does no such thing. Instead, functions that can fail have a return value and any exceptional conditions are signalled by a special return value, which you need to check from the documentation of the given function. In case of getchar, the documentation from the C11 standard says (C11 7.21.7.6p3):
The getchar function returns the next character from the input stream pointed to by stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and getchar returns EOF. If a read error occurs, the error indicator for the stream is set and getchar returns EOF.
It is stated elsewhere that EOF is an integer constant that is < 0, and any ordinary return value is >= 0 - the unsigned char zero-extended to an int.
The stream being at end-of-file means that all of the input has been consumed. For standard input it is possible to cause this from keyboard by typing Ctrl+D on Unix/Linux terminals and Ctrl+Z in Windows console windows. Another possibility would be for the program to receive the input from a file or a pipe instead of from keyboard - then end-of-file would be signalled whenever that input were fully consumed, i.e.
cat file | ./myprogram
or
./myprogram < file
As the above fragment says, there are actually two different conditions that can cause getchar to return EOF: either the end-of-file was reached, or an actual error occurred. This cannot be deduced from the return value alone. Instead you must use the functions feof and ferror. feof(stdin) would return a true value if end-of-file was reached on the standard input. ferror(stdin) would return true if an error occurred.
If an actual error occurred, the variable errno defined by <errno.h> would contain the error code; the function perror can be used to automatically display a human readable error message with a prefix. Thus we could expand the example to
#include <stdio.h>
#include <errno.h> // for the definition of errno
#include <stdlib.h> // for exit()
int main(void)
{
int c;
while ((c = getchar()) != EOF)
putchar(c);
if (feof(stdin)) {
printf("end-of-file reached\n");
exit(0);
}
else if (ferror(stdin)) {
printf("An error occurred. errno set to %d\n", errno);
perror("Human readable explanation");
exit(1);
}
else {
printf("This should never happen...\n");
exit('?');
}
}
To trigger the end-of-file, one would use Ctrl+D (here displayed as ^D) on a new line on Linux:
% ./a.out
Hello world
Hello world
^D
end-of-file reached
(notice how the input here is line-buffered, so the input is not interleaved within the line with output).
Likewise, we can get the same effect by using a pipeline.
% echo Hello world | ./a.out
Hello world
end-of-file reached
To trigger an error is a bit more tricky. In bash and zsh shells the standard input can be closed so that it doesn't come from anywhere, by appending <&- to the command line:
% ./a.out <&-
An error occurred. errno set to 9
Human readable explanation: Bad file descriptor
Bad file descriptor, or EBADF means that the standard input - file descriptor number 0 was invalid, as it was not opened at all.
Another fun way to generate an error would be to read the standard input from a directory - this causes errno to be set to EISDIR on Linux:
% ./a.out < /
An error occurred. errno set to 21
Human readable explanation: Is a directory
Actually the return value of putchar should be checked too - it likewise
returns EOF on error, or the character written:
while ((c = getchar()) != EOF) {
if (putchar(c) == EOF) {
perror("putchar failed");
exit(1);
}
}
And now we can test this by redirecting the standard output to /dev/full - however there is a gotcha - since standard output is buffered we need to write enough to cause the buffer to flush right away and not at the end of the program. We get infinite zero bytes from /dev/zero:
% ./a.out < /dev/zero > /dev/full
putchar failed: No space left on device
P.S. it is very important to always use a variable of type int to store the return value of getchar(). Even though it reads a character, using signed/unsigned/plain char is always wrong.
Maybe you got confused by the fact that entering -1 on the command line does not end your program? Because getchar() reads this as two chars, - and 1. In the assignment to c, the character is converted to the ASCII numeric value. This numeric value is stored in some memory location, accessed by c.
Then putchar(c) retrieves this value, looks up the ASCII table and converts back to character, which is printed.
I guess finding the value -1 decimal in the ASCII table is impossible, because the table starts at 0. So getchar() has to account for the different solutions at different platforms. maybe there is a getchar() version for each platform?
I just find it strange that this EOF is not in the regular ascii. It could have been one of the first characters, which are not printable. For instance, End-of-line is in the ASCII.
What happens if you transfer your file from windows to linux? Will the EOF file character be automatically updated?
getchar() function reads a character from the keyboard (ie, stdin)
In the condition inside the given while loop, getchar() is called before each iteration and the received value is assigned to the integer c.
Now, it must be understood that in C, the standard input (stdin) is like a file. ie, the input is buffered. Input will stay in the buffer till it is actually consumed.
stdin is actually the standard input stream.
getchar() returns the the next available value in the input buffer.
The program essentially displays whatever that was read from the keyboard; including white space like \n (newline), space, etc.
ie, the input is the input that the user provides via the keyboard (stdin usually means keyboard).
And the output is whatever we provide as input.
The input that we provide is read character by character & treated as characters even if we give them as numbers.
getchar() will return EOF only if the end of file is reached. The ‘file’ that we are concerned with here is the stdin itself (standard input).
Imagine a file existing where the input that we provide via keyboard is being stored. That’s stdin.
This ‘file’ is like an infinite file. So no EOF.
If we provide more input than that getchar() can handle at a time (before giving it as input by pressing enter), the extra values will still be stored in the input buffer unconsumed.
The getchar() will read the first character from the input, store it in c and printcwithputchar(c)`.
During the next iteration of the while loop, the extra characters given during the previous iteration which are still in stdin are taken during while ((c = getchar()) != EOF) with the c=getchar() part.
Now the same process is repeated till there is nothing left in the input buffer.
This makes it look as if putchar() is returning a string instead of a single character at a time if more than one character is given as input during an iteration.
Eg: if input was
abcdefghijkl
the output would’ve been the same
abcdefghijkl
If you don’t want this behaviour, you can add fflush(stdin); right after the putchar(c);.
This will cause the loop to print only the first character in the input provided during each iteration.
Eg: if input was
adgbad
only a will be printed.
The input is sent to stdin only after you press enter.
putchar() is the opposite of getchar(). It writes the output to the standard output stream (stdout, usually the monitor).
EOF is not a character present in the file. It’s something returned by the function as an error code.
You probably won’t be able to exit from the give while loop normally though. The input buffer will emptied (for displaying to the output) as soon as something comes into it via keyboard and the stdin won't give EOF.
For manually exiting the loop, EOF can be sent using keyboard by pressing
ctrl+D in Linux and
ctrl+Z in Windows
eg:
while ((c = getchar()) != EOF)
{
putchar(c);
fflush(stdin);
}
printf("\nGot past!");
If you press the key combination to give EOF, the message Got past! will be displayed before exiting the program.
If stdin is not already empty, you will have to press this key combination twice. Once to clear this buffer and then to simuate EOF.
EDIT: The extra pair of parenthesis around c = getchar() in while ((c = getchar()) != EOF) is to make sure that the value returned by getchar() is first assigned to c before that value is compared with EOF.
If this extra parenthesis were not there, the expression would effectively have been while (c = (getchar() != EOF) ) which would've meant that c could have either of 2 values: 1 (for true) or 0 (for false) which is obviously not what is intended.
getchar()
gets a character from input.
c = getchar()
The value of this assignment is the value of the left side after the assignment, or the value of the character that's been read. Value of EOF is by default -1.
((c = getchar()) != EOF)
As long as the value stays something other than EOF or, in other words, as long as the condition stays true, the loop will continue to iterate. Once the value becomes EOF the value of the entire condition will be 0 and it will break the loop.
The additional parentheses around c = getchar() are for the compiler, to emphasize that we really wanted to do an assignment inside the condition, because it usually assumes you wanted to type == and warns you.
main() {
int c;
while ((c = getchar()) != EOF)
putchar(c);
}
So the entire code actually echoes back what you input. It assigns the value of the characters to c inside the condition and then outputs it back in the body of the loop, ending only when the end of file is detected.
In a similar manner to the | pipe command above you can use redirection on your system to utilize the above code to display all the character contents of a file, till it reaches the end (EOF) represented by CTRL-Z or CTRL-D usually.
In console:
ProgramName < FileName1.txt
And to create a copy of what is read from FileName1 you can:
ProgramName < FileName1.txt > CopyOfInput.txt
This demonstrates your program in multiple ways to hopefully aid your understanding.
-Hope that helps.
main(){
int c;
while ((c = getchar()) != EOF)
putchar(c);
}
Actually c=getchar() provides the character which user enters on the console and that value is checked with EOF which represents End Of File . EOF is encountered at last of file. (c = getchar()) != EOF is equivalent to c != EOF . Now i think this is much easier . If you any further query let me know.
#include <stdio.h>
/* copy input to output; 2nd version*/
main()
{
int c;
while ((c = getchar()) != EOF)
putchar(c);
}
this is very confusing... since you never escape the while loop. I've learned that EOF is -1. i type -1 but it just reprints it. It's a never ending loop. Over time did the library get changed and differs from what the book intended it to be? when i say library i mean the putchar()/getchar() that's in the library... sorry.
How EOF(end of file ) works?
EOF is simply a macro designating a negative value. It doesn't have to be -1. You can signal end-of-file from the command line with a control character, usually a combination of ctrl+z for Windows systems or ctrl+d for POSIX systems.
when you write '-1', you do not write the VALUE -1, but the character string { '-', '1' }
take a look here.
EOF is not a character
This is important. Remember it.
When you try to get a character, several things may happen. The usual is to effectively read a character: your program receives that character and goes on its way ...
int ch = getchar();
but, what happens is the disk crashes? or there's a bad sector just at that point? or the network goes down? or there is no more data?
Well, then there must be a way to differentiate these conditions from plain characters. The way chosen by C is to return a value that can NEVER be interpreted as a real character. That value is EOF, which is a negative value (all real characters are returned with their value converted to unsigned char even if your implementation uses signed char for char). That is also why it is very important to use int for characters (not char as would be expected).
So EOF means that it was impossible to read a character. You can try to figure out why (network down? bad sector? end of file? ...) or simply assume it was end-of-file and go from there.
So, in
while ((c = getchar()) != EOF)
there are two things: an assignment and a comparison
c = getchar()
will put a value of 0 or more in c for real characters or EOF if there's an error, therefore
while ((c = getchar()) != EOF)
means "while there is no error getting characters into variable c"
Important thing to remember:
EOF is not a character. Define characters with int.
After entering text, hit the Enter key for a new line. Then hold down Ctrl and press the letter D.
I'm working on the same book. I think you should be able to just hit Ctrl+D to exit, but I had to hit Enter first (I think there is something wrong with my shell).
That's in the chapter text, by the way.