Reading from stdin

[C GIllespie]

Dear All,

I have a C program that prints out numbers 1 to 10 to stdout. I wish to pipe
this into a python script to print out the numbers, e.g. ./myCProg |
myPython.py

However, I want the python script to print out the numbers as it gets them,
since there could be hours/days between numbers - not a very efficient C
program :). Actually, I would like to read-a-line/ print-a-line/
read-a-line/etc

I have tried things like 'sys.stdin.read *' with no success.

Thanks

Colin

[Christian Vogel]

Re: Reading from stdin

C GIllespie wrote:[color=blue]
> efficient C program :). Actually, I would like to read-a-line/
> print-a-line/ read-a-line/etc[/color]

probably both your C- and your python scripts use buffered output. So the
C-program will not print line-by-line but rather en-block after many bytes
of output have accumulated.

In your C-program, do this (that's most likely your problem):

printf("%f\n",x ); /* print valuable data */
fflush(stdout); /* make sure it's written to stdout */

In your python-program, do this (that's probably not your problem):

print "%f"%x # print valueable data
sys.stdout.flus h() # make sure it's written to stdout

Chris

[Skip Montanaro]

Re: Reading from stdin


Colin> However, I want the python script to print out the numbers as it
Colin> gets them, since there could be hours/days between numbers - not
Colin> a very efficient C program :). Actually, I would like to
Colin> read-a-line/ print-a-line/ read-a-line/etc

Colin> I have tried things like 'sys.stdin.read *' with no success.

Have you tried this?

import sys
for line in sys.stdin:
print line.strip()

Skip

[C GIllespie]

Re: Reading from stdin

> probably both your C- and your python scripts use buffered output. So
[color=blue]
> the C-program will not print line-by-line but rather en-block after[/color]
[color=blue]
> many bytes of output have accumulated.[/color]
[color=blue]
>[/color]
[color=blue]
> In your C-program, do this (that's most likely your problem):[/color]
[color=blue]
>[/color]
[color=blue]
> printf("%f\n",x ); /* print valuable data */[/color]
[color=blue]
> fflush(stdout); /* make sure it's written to stdout */[/color]

Yep, that was the problem.

Thanks

Colin

[P@draigBrady.com]

Re: Reading from stdin

Skip Montanaro wrote:[color=blue]
> Colin> However, I want the python script to print out the numbers as it
> Colin> gets them, since there could be hours/days between numbers - not
> Colin> a very efficient C program :). Actually, I would like to
> Colin> read-a-line/ print-a-line/ read-a-line/etc
>
> Colin> I have tried things like 'sys.stdin.read *' with no success.
>
> Have you tried this?
>
> import sys
> for line in sys.stdin:
> print line.strip()[/color]

That's block buffered. More details here:

http://www.pixelbeat.org/readline/python

Pádraig.