Thread: printing a tab

Code:

#include <stdio.h>

int main()
{
    char c = '  '; /* I typed tab here */
    printf("a%ca\n", c);
    return 0;
}

I m using devc++.
The output of the program is : "a a". There is one space between the alphas. Why isn't there a tab?

you're assigning a character constant to the variable that you're printing. As ' ' represents a single whitespace, regardless of just how much white space you throw in there, and so it will only print a single whitespace.

You can either use a string to represent the tab, or the escape sequence that represents the tab.

Code:

#include <stdio.h>

int main(void)
{
    char *c = "		"; 
    printf("a%sa\n", c);
    return 0;
}

or

Code:

#include <stdio.h>

int main(void)
{
    char c = '\t';
    printf("a%ca\n", c);
    return 0;
}

Also, just so you know, you really should use void if there are no arguments to main. Without the void, it translates as "there is an unknown amount of arguments".

FAQ Entry

Edit: Beaten

thanks for the replys. i tried the same code (the one i posted) in cygwin (gcc) and the output was :
"a a" (a [tab] a). can anyone explain why this difference?

i didn't catch your post itsme86. It is probably the devc++ editor's fault. is the newline considered a single character?

Code:

c = '
';

Originally Posted by itsme86

That's true, but not wholly the case.

My mistake, thanks for the info

ok, i know about the escape sequences \n \t \r etc. But i m asking: considering that newline is a single character is the following acceptable?

Code:

char c = '
';

the reason i m asking is because i m writing a lexical analyser and i want to know whether the analyser should accept it or not.

i m using flex to write the lexical analyser and i have the following prob:
this code

Code:

//other stuff for flex

int main ()
{
	int token;
	
	do { 
		token = yylex();
		printf( "token = %d, lexeme = \"%s\"\n", token, yytext );
	} while ( token != T_eof );
	
	return 0;
}

when i input a tab character

Code:

'         '

gives

Code:

token = 39, lexeme = "' '"

this code

Code:

//exactly the same other stuff for flex

int main ()
{
	int token;
	
	do { 
		token = yylex();
		putchar('a');
		printf( "token = %d, lexeme = \"%s\"\n", token, yytext );
	} while ( token != T_eof );
	
	return 0;
}

when i input a tab character gives

Code:

atoken = 39, lexeme = "'        '"

the single thing i change is the putchar('a')
does anyone have an idea why that happens?

i used gdb to debug.

Code:

Hardware access (read/write) watchpoint 3: yytext

Value = 0x93c70 "'\t'"
0x00003c38 in main () at lexin.c:107
107                        printf( "token = %d, lexeme = \"%s\"\n", token, yytex
t );
(gdb) print yytext
$2 = 0x93c70 "'\t'"
(gdb) c
Continuing.
token = 39, lexeme = "' '"

how is that possible? the value of yytext is "'\t'" but printf prints "' '".

ok i got it. I was thinking of a tab as many spaces. But printf doesn't print many spaces, it moves to the next tab stop. So i was thinking that printf makes a mistake when it prints a single space,but it was simply because the next tab stop was a single space away. thanx for the replies.