Remember Me? Thread: Is there an inkey in C. Is there an inkey in C. Is it possible to write in c what I have paraphrased below? It depends on your OS and Compiler. If you're looking for something to test if there has been a key press, not to wait if there hasn't, and not to wait for a newline.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut. If at first you don't succeed, try writing your phone number on the exam paper.
Checking whether there has been a keypress is not the issue.
I am looking for a similar statement as inkeythe equivalent of which statement doesn't appear to be in C. Since, you will not tell us what inkey means to you there is no way to help you! Tim S. They are,in short, a perfect match.
It's a truly stupid question. If you want the truth to stand clear before you, never be for or against. The function of interest isn't in C because of the nature of C. It was originally purpose built to write the UNIX operating system while translating the assembler source into a language operating near the assembler level without no CPU dependencies.
Instead, it relies upon third party libraries, and in your example case one that spans a diverse range of hardware. If the concept of inkey is to examine what current keyboard button is being held down, that is rather specific to a device like the PC. The original C viewed input as a specialized type of device opened as a file, which you know as stdin or stdout for outputand doesn't function in a related way.
Where, in the console, a keystroke is data sent through a serial connection, and is therefore a keystroke result, on a PC the notion is far more interesting, related to the fact that the keyboard hardware is more closely tied to the computer the software is running on. Most specifically, there are ways to detect combinations of keys being held, when they are pressed and when they are released.
It only takes a minute to sign up. By default SIGINT the interrupt signal kills the foreground application, but the application can catch the signal and react in some different way for example, the shell itself catches the signal and aborts the line you've begun typing, but it doesn't exit, it shows a new prompt and waits for a new command line. This is rarely useful. Sign up to join this community. The best answers are voted up and rise to the top.
How to signal the end of stdin input Ask Question. Asked 9 years ago. Active 2 years, 2 months ago. Viewed k times. In Bash, I learned that the ending signal can be changed by here document. But by default how can I signal the end of stdin input? So am I wrong?
Tim Tim Active Oldest Votes. Gilles 'SO- stop being evil' Gilles 'SO- stop being evil' k gold badges silver badges bronze badges. Tim: it's lower case you want Yes this is confusing sometimes.
Caleb: Thanks! How shall one specify that the key is in capital? Or is there ever such case? It does not send a character to the program. The shell is not involved at all. Your second point lumps two completely different things together.Remember Me? Thread: Reading Ctrl D in fgets with some inputs. Reading Ctrl D in fgets with some inputs. Hi to all, I was wondering if you guys can help me with this tricky stdin problem?
Suppose I want my c program to accept input. But at the same time I want to detect Ctrl D as well. How do I detect Ctrl D if there are characters before it? For the record, I am able to detect Ctrl D by itself. So test for EOF. It's always 4. K always 4 then, how about a solution?? All problems in computer science can be solved by another level of indirection, except for the problem of too many layers of indirection.
Magestrium it is against forum rules to provide someone with the entire solution tp his problem before he even got to start working on it. So please don't lecture me. Besides, your solution is poor mainly due to reasons pointed above by vart.
When using redirection from a file to stdin, there is no extra effort to signal the end of stdin input. How does the program knows the end of stdin input? When using pipe to direct stdout output from another program to the stdin input of the program, there is no extra effort to signal the end of stdin input?
In some programs, such as bcwhenever you enter an arithmetic expression and hit return, it will takes in the expression as stdin input and output the evaluated result. In such case, is each line ended by return considered a whole stdin input, or are all the lines typed from starting bc till exiting bc considered a stdin input?
When do we need to specify the end of stdin input explicitly like for here-document, and when do we need not? Digging around with strace may be necessary to see exactly what some higher-level function like getline 3 or specific application is doing under the hood, but most things will probably boil down to read 2 or feof 3.
The heredoc end-label is completely optional in a shell script though is necessary if other code will follow. Sign up to join this community. The best answers are voted up and rise to the top. How does a program detect the end of stdin input? Ask Question. Asked 4 years, 4 months ago. Active 4 years, 4 months ago.C Programming Tutorial - 51 - How to Read Files
Viewed 1k times. There are several ways of providing stdin input to a program. What is the general principle that a program knows how to detect the end of stdin input? Are they program-dependent, or program-independent? Tim Tim See pubs.
C - Input and Output
Happily recall a sibling question unix. Active Oldest Votes. Is feof 3 implemented based on read 2 to detect eof? Tim - fopenfreadfeofetc. These are built on top of the openreadetc.
Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Does stdin have any EOF?
Nim: Check if stdin/stdout are associated with terminal or pipe
For example, if I start reading from stdin using fread or readthen will the following loop end? In console you can simulate EOF flag. When you type this in the console, program will behave like it has just reached end of input file. Actually -- yes. One may consider stdin not redirected, but taken from the console as infinite file -- no one can tell where does it end.
You don't say the type of c but using that name implies that it's a char. Note that the EOF value for iosteams is an int Storing that into an unsigned char will get you a value of which will not match EOF.
First getchar is really getc stdin so getc FILE you can read more from that. Say in a program I call getchar at first the stdin is empty so it pauses for input. I do believe stdin is a global so until getchar or similar function gets called it to clear the stream the characters remain there which can cause bugs later if you use getchar elsewhere. As people have mentioned you can use gets char which puts all characters until newline into the character array.
The problem with this is you need a char larger than input or you will get errors. The nice thing is gets char does clear stdin so you can make a dumby buffer to clear stdin or process it. Learn more. Asked 10 years ago. Active 1 month ago. Viewed 42k times. Andreas Wenzel 2, 1 1 gold badge 3 3 silver badges 18 18 bronze badges. Ravi Gupta Ravi Gupta 5, 14 14 gold badges 49 49 silver badges 74 74 bronze badges.
EOF, getc() and feof() in C
Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I am using the following C code to take input from user until EOF occurs, but problem is this code is not working, it terminates after taking first input. Can anyone tell me whats wrong with this code. Thanks in advance. EOF is just a macro with a value usually You have to test something against EOFsuch as the result of a getchar call.
In your example you should probably check the return value of scanf and if this indicates that no fields were read, then check for end-of-file. EOF is a constant in C.
You are not checking the actual file for EOF. You need to do something like this. Here is the documentation to feof. You can also check the return value of scanf. It returns the number of successfully converted items, or EOF if it reaches the end of the file. If the user types something that can't be interpreted as a C floating-point number, like "pi", the scanf call will not assign anything to inputand won't progress from there.
This means it would attempt to keep reading "pi", and failing. Given the change to while! This will remove the next string from the input stream up to 99 characters, anyway - the extra char is for the null terminator on the string. You know, this is reminding me of all the reasons I hate scanfand why I use fgets instead and then maybe parse it using sscanf. You want to check the result of scanf to make sure there was a successful conversion; if there wasn't, then one of three things is true:.
Learn more. Asked 10 years, 10 months ago. Active 4 years, 11 months ago. Viewed k times. Jens The EOF macro represents a negative value that is used to indicate that the file is exhausted and no data remains when reading data from a file. EOF is an example of an in-band error indicator. In-band error indicators are problematic to work with, and the creation of new in-band-error indicators is discouraged by ERRC.
Avoid in-band error indicators. Represent characters using an appropriate type. If a read error occurs, the error indicator for the stream is set and the function returns EOF. If these functions succeed, they cast the character returned into an unsigned char.
Because EOF is negative, it should not match any unsigned character value. However, this is only true for implementations where the int type is wider than char. On an implementation where int and char have the same width, a character-reading function can read and return a valid character that has the same bit-pattern as EOF.
This could occur, for example, if an attacker inserted a value that looked like EOF into the file or data stream to alter the behavior of the program. This problem is much more common when reading wide characters.
This value can represent the next wide character read, or it can represent WEOFwhich indicates end-of-file for wide character streams. Similarly, all UTF characters are positive when viewed as a signed bit integer. All widely used character sets are designed with at least one value that does not represent a character.
Consequently, it would require a custom character set designed without consideration of the C programming language for this problem to occur with wide characters or with ordinary characters that are as wide as int.
The C Standard feof and ferror functions are not subject to the problems associated with character and integer sizes and should be used to verify end-of-file and file errors for susceptible implementations [ Kettlewell ].
Calling both functions on each iteration of a loop adds significant overhead, so a good strategy is to temporarily trust EOF and WEOF within the loop but verify them with feof and ferror following the loop. Although EOF is guaranteed to be negative and distinct from the value of any unsigned character, it is not guaranteed to be different from any such value when converted to an int. Consequently, when int has the same width as charthis loop may terminate prematurely.
This compliant solution uses feof and ferror to test whether the EOF was an actual character or a real EOF because of end-of-file or errors:.
This noncompliant code example uses an assertion to ensure that the code is executed only on architectures where int is wider than char and EOF is guaranteed not to be a valid character value.
However, this code example is noncompliant because the variable c is declared as a char rather than an intmaking it possible for a valid character value to compare equal to the value of the EOF macro when char is signed because of sign extension:. See STRC. Cast characters to unsigned char before converting to larger integer sizes.
This compliant solution declares c to be an int. Consequently, the loop will terminate only when the file is exhausted. This code suffers from two problems. Both of these problems make it possible for an attacker to terminate the loop prematurely by supplying the wide-character value matching WEOF in the file.
Furthermore, it does not rely on WEOF to determine end-of-file definitively. These functions include fclosefflushfputsfscanfputsscanfsscanfvfscanfand vscanf. These return values can be compared to EOF without validating the result.
Incorrectly assuming characters from a file cannot match EOF or WEOF has resulted in significant vulnerabilities, including command injection attacks. Coverity Prevent cannot discover all violations of this rule, so further verification is necessary.
Polyspace Bug Finder. Checks for character values absorbed into EOF rule partially covered.