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getchar() not working according to the code [message #1853151]

Mon, 20 June 2022 16:37

C Lehar

Messages: 2
Registered: June 2022

Junior Member

I am new to C language. I'm learning scanf() and getchar() statements but always have trouble while exceuting them. getchar() is not taking input as per the flow of the code, instead first the character input is taken and then rest of the code follows. For example: The code is:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

int main(void) {
char c = 'A';
printf("%c\n",c);
printf("%d\n",c);
printf("%0x\n",c);

printf("Input a character\n");
c = getchar();
printf("You entered %c\n",c);

return EXIT_SUCCESS;
}
But the output first takes a character input and the rest of it executed, If my char input is h, the output is :
h
A
65
41
Input a character
You entered h.

I was having similar problems with scanf(), but using fflush(stdout), after scanf() statement worked. Here fflush is not working and I am not able to figure out. Please help.

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Re: getchar() not working according to the code [message #1853171 is a reply to message #1853151]

Tue, 21 June 2022 16:16

tepalia02 02

Messages: 21
Registered: April 2022

Junior Member

Have you tried changing the variable's name? I mean you have written:

char c = 'A';

and again written the same variable

c = getchar();

Both are the same variables. Have you tried with a different name in any of these two lines?

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Re: getchar() not working according to the code [message #1853196 is a reply to message #1853171]

Wed, 22 June 2022 13:36

C Lehar

Messages: 2
Registered: June 2022

Junior Member

Yes, changing the variable name also gives the same results as before.

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Re: getchar() not working according to the code [message #1853450 is a reply to message #1853196]

Sat, 02 July 2022 17:18

tepalia02 02

Messages: 21
Registered: April 2022

Junior Member

I tried in online C compiler. I got the following output.

A
65
41
Input a character
h
You entered h

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Re: getchar() not working according to the code [message #1854156 is a reply to message #1853450]

Wed, 03 August 2022 19:55

timothy johnson

Messages: 3
Registered: August 2022

Junior Member

C (and other languages) use Streams for Input and Output. The streams can have buffers associated with them that prevent the transfer of data until the buffer is full, or some other action forces the transfer.

Your problem has nothing to do with scanf() or getchar(). Your issue is that the buffer for the output stream is set to some relatively large value. I think Eclipse defaults to 1000 characters. Your printf() statements are placed into the stream as expected, but nothing is transferred until the program completes because the buffer was never full.

You can find the correct setting in Eclipse to reduce the buffer size but I always advise students to choose a solution that should always work. For <stdio> you can use the command setbuf(stdout, NULL); prior to your first printf() statement. This sets the buffer size to 0 (NULL) and forces immediate transfer of the Output stream.

The reason the online compiler worked properly is that it's buffer size was set to 0 by default (which you would expect)

Note - for some embedded systems setting the buffer size to 0 can cause slowed response

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