alternative for getchar in Linux ?

[casp3r]

Hello forumers,

So i had this problem since my first C programming class, and i did a google search and try to replace getchar() with fgetc and others and it just not work. So here is the sample of exercise that i'm working on now.

The system waits for price of an item from the user, and ask whether there is another item by pressing 'y' || 'Y'. This is when i used the function of getchar and it doesn't work. It doesn't wait for input from the user

Can anybody tell me what i'm doing wrong here ?

P/s : its working well in Windows

#include <stdio.h>


void main ()
{
	
	void checkout();
	char morecust;
	//int getchar(void);	
	
	do
	{
		system("clear");
		checkout();		//function call
		printf("\n\n\tAnother customer? ");
		morecust=getchar();fflush(stdin);
	}
	while(morecust=="y" || morecust=="Y");
}

void checkout()
{

	float price,total=0;
	char moreitem;
	//int getchar(void);

	do
	{
		printf("\n\n\tEnter price :");
		scanf("%f",&price);
		total+=price;
		printf("\n\n\tAnother item?");
		moreitem=getchar();fflush(stdin);
	}
	while(moreitem=='y' || moreitem=='Y');
	printf("\n\n\tAmount %.2f: ",total);
	printf("\n\n\tTax %.2f: ",total*0.05);
	printf("\n\n\tTotal amt %.2f: ",total + (total*0.05));

}

[Fenrin]

a few month ago I tried to find a replacement for getch() (under Windoze you must include conio.h to use getch()).
Under Linux it looks like this:

#include <unistd.h> 
#include <termios.h>

int getch(void)
{
    int ch;
    struct termios oldt;
    struct termios newt;
    tcgetattr(STDIN_FILENO, &oldt); /*store old settings */
    newt = oldt; /* copy old settings to new settings */
    newt.c_lflag &= ~(ICANON | ECHO); /* make one change to old settings in new settings */
    tcsetattr(STDIN_FILENO, TCSANOW, &newt); /*apply the new settings immediatly */
    ch = getchar(); /* standard getchar call */
    tcsetattr(STDIN_FILENO, TCSANOW, &oldt); /*reapply the old settings */
    return ch; /*return received char */
}

the difference between getchar() and getch() is that it works without the return key. Above code doesn't work under windoze.

Is this function any help for you?

[casp3r]

Thanks for clarify this, i have two questions here.

int getch(void)

why did you use void , because since we create a new function called "getch" so it surely takes something (value) right ?

int ch;

should i change it to the char since i'm accepting the character here ?

sadly, the code still doesn't make any difference



Sorry, i'm still a noob

Here is how i did it :

#include <stdio.h>
#include <unistd.h> 
#include <termios.h>

void main ()
{
	
	void checkout();
	char morecust;
		
	
	do
	{
		system("clear");
		checkout();		//function call
		printf("\n\n\tAnother customer? ");
		morecust=getch();fflush(stdin);
	}
	while(morecust=="y" || morecust=="Y");
}

void checkout()
{

	float price,total=0;
	char moreitem;
	

	do
	{
		printf("\n\n\tEnter price :");
		scanf("%f",&price);
		total+=price;
		printf("\n\n\tAnother item?");
		moreitem=getch();fflush(stdin);

	}
	while(moreitem=="y" || moreitem=="Y");
	

	printf("\n\n\tAmount %.2f: ",total);
	printf("\n\n\tTax %.2f: ",total*0.05);
	printf("\n\n\tTotal amt %.2f: ",total + (total*0.05));
	
}

int getch(void)
{
    int ch;
    struct termios oldt;
    struct termios newt;
    tcgetattr(STDIN_FILENO, &oldt); /*store old settings */
    newt = oldt; /* copy old settings to new settings */
    newt.c_lflag &= ~(ICANON | ECHO); /* make one change to old settings in new settings */
    tcsetattr(STDIN_FILENO, TCSANOW, &newt); /*apply the new settings immediatly */
    ch = getchar(); /* standard getchar call */
    tcsetattr(STDIN_FILENO, TCSANOW, &oldt); /*reapply the old settings */
    return ch; /*return received char */
}

and return this :

Enter price :50


	Another item?

	Amount 50.00: 

	Tax 2.50: 

	Total amt 52.50: 

	Another customer?

[aleph]

TO the OP: your code probably won't work under any system anyway. The problem is that you're comparing morecust to (the address of ) a literal string, in the while condition. And morecust should be int, there's no reason to cast it into char and cast back when comparing with the return value of getchar().

Just don't surround the "y" and "Y" characters with double quotes. Use the single quotes, which tells the compiler here's an int literal, not a string.

[casp3r]

Originally Posted by aleph

TO the OP: your code probably won't work under any system anyway. The problem is that you're comparing morecust to (the address of ) a literal string, in the while condition. And morecust should be int, there's no reason to cast it into char and cast back when comparing with the return value of getchar().

Just don't surround the "y" and "Y" characters with double quotes. Use the single quotes, which tells the compiler here's an int literal, not a string.

Thanks for correcting me that, but this system does work on Windows, because this code directly copied from my lecturer in the class today and its working well on her machine, even after changed double quote with single, the results still the same. actually i have done 4-5 system using getchar() function and none of them are waiting for user input. If only my lecturer knows how to use Linux, i'd have asked her tho

---------- Post added at 11:41 PM ---------- Previous post was at 11:38 PM ----------

Here is the code directly from my lecturer :

(i removed conio.h and Windows.h)

//POS at grocery store
#include<stdio.h>



void main()
{
	void checkout(); //function prototype
	char ans;
	do
	{
		system("clear");
		checkout();  //function call returning back total
		printf("\n\n\t Another customer?:");
		ans=getchar();fflush(stdin);
	}while(ans=='y' || ans=='Y');
}
//function definition
void checkout()
{
	float price,total=0;
	char con;
	do
	{
		printf("\n\n\t Enter price: ");
		scanf("%f",&price);fflush(stdin);
		total+=price;
		printf("\n\n\t Another item ?:");
		con=getchar();fflush(stdin);
	}while(con=='y' || con=='Y');
	printf("\n\n\t   Amount %.2f: ",total);
	printf("\n\n\t      Tax %.2f: ",total*.05);
	printf("\n\n\tTotal amt %.2f: ",total + total*.05);
	
}

[Skull One]

The problem is not with 'getchar', but with 'fflush': it only works for _output_ streams.
For _input_ you can use '__fpurge' (from "stdio_ext.h"), or some function:

/* Discard rest of input line. */
int c;
while (c != '\n' && c != EOF)
        c = fgetc (stdin);

Ref:
info fflush
info __fpurge
info getchar

[jpollard]

The real issue is the scanf. It reads the input number, and stops on the first non-numeric value.

In this case, that value is a newline - it has not been processed yet.

When you do the "con=getchar()", what is returned is the newline.

Since the newline character is neither 'y' or 'Y', it terminates the checkout function.

Now, adding a "\n" to the format scan would terminate the line... but buffer handling gets strange. Now you are fighting both stdin buffering and stdout buffering. (the prompt for the next input doesn't occur because the scanf is waiting for the buffer...)

This problem is caused by mixing both buffered I/O and wanting non-buffered operation (sometimes).

This CAN work, but only on systems that don't use buffered I/O in the library... and I believe that is how windows does its unix "compatibility" (which isn't really compatible).

You would do better to have your own I/O (and any buffering you do/don't want.

the following will "work" for most systems:

//POS at grocery store
#include <stdio.h>
#include <stdlib.h>

void main(void)
{
        void checkout(void); //function prototype
        char ans;
        do
        {
                system("clear");
                checkout();  //function call returning back total
                printf("\n\n\t Another customer?:");
                fflush(stdout);
                while ((ans=getchar()) == '\n');
        }while(ans=='y' || ans=='Y');
}
//function definition
void checkout(void)
{
        float price,total=0;
        char con;
        do
        {
                printf("\n\n\t Enter price: ");
                fflush(stdin);
                scanf("%f",&price);
                total+=price;
                printf("\n\n\t Another item ?:");
                fflush(stdin);
                while ((con = getchar()) == '\n');
fprintf(stdout,"con=%d",con);
        }while(con=='y' || con=='Y');
        printf("\n\n\t   Amount %.2f: ",total);
        printf("\n\n\t      Tax %.2f: ",total*.05);
        printf("\n\n\tTotal amt %.2f: ",total + total*.05);

}

Note: the use of fflush(stdout) is reasonable, but most UNIX like systems don't need it when stdin/stdout is connected to a terminal.

The change is to replace the simple "xx=getchar" line with "while ((xx=getchar()) == '\n');" This causes the input to skip the terminating newline.

This is still not exactly reasonable - data lines like "25.5 and more" will not be processed correctly as the space following the 25.5 will terminate the loop, and the test for y or Y will fail (using the " ") and the outer loop for new customers will fail on the "a" of "and more".

There are a lot of "improper input" handling that isn't done.

[Skull One]

Originally Posted by jpollard

The real issue is the scanf. It reads the input number, and stops on the first non-numeric value.

In this case, that value is a newline - it has not been processed yet.

When you do the "con=getchar()", what is returned is the newline.

Since the newline character is neither 'y' or 'Y', it terminates the checkout function.

Now, adding a "\n" to the format scan would terminate the line... but buffer handling gets strange. Now you are fighting both stdin buffering and stdout buffering. (the prompt for the next input doesn't occur because the scanf is waiting for the buffer...)

This problem is caused by mixing both buffered I/O and wanting non-buffered operation (sometimes).

This CAN work, but only on systems that don't use buffered I/O in the library... and I believe that is how windows does its unix "compatibility" (which isn't really compatible).

You would do better to have your own I/O (and any buffering you do/don't want.

We're saying the same: the stdin is not emptied.
It works fine using __fpurge.

[jpollard]

The __fpurge doesn't exist on some systems as it is definitely a non-standard function.

[Skull One]

Originally Posted by jpollard

The __fpurge doesn't exist on some systems as it is definitely a non-standard function.

You're right.
That's why we could also define a procedure to do the job, like the one used in the example of 'info getchar'.

[RupertPupkin]

I like Fenrin's solution, which is similar to the one here: http://wesley.vidiqatch.org/code-sni...tche-on-linux/

[jpollard]

For unix based systems fenrin's solution will work. But again, not all systems have the tcgetattr libraries.

For basic classwork (which this looks like) it would be much better to implement a local function that does what you want. The example shown in "info getchar" is much more flexible (slightly reformatted):

int y_or_n_p (const char *question)
{
    fputs (question, stdout);
    while (1) {
        int c, answer;
        /* Write a space to separate answer from question. */
        fputc (' ', stdout);
        /* Read the first character of the line.
        This should be the answer character, but might not be. */
        c = tolower (fgetc (stdin));
        answer = c;
        /* Discard rest of input line. */
        while (c != '\n' && c != EOF)
            c = fgetc (stdin);
        /* Obey the answer if it was valid. */
        if (answer == 'y') return 1;
        if (answer == 'n') return 0;
        /* Answer was invalid: ask for valid answer. */
        fputs ("Please answer y or n:", stdout);
    }
}

[casp3r]

THANKS FOR ALL THOSE WHO HELPED ME CLARIFY THIS MATTER

Fenrin
jpollard
Skull One

Now i understand why and thanks for post some 'tricks' that can overcome this default buffer issue.

oh, and RupertPupkin, thanks for bringing up this useful article

http://wesley.vidiqatch.org/code-sni...tche-on-linux/

Linux FTW!