program accept argument from both stdin and command line

[spskhokhar]

/*
* program accept argument from stdin as well as command line
* run it with
* echo "1 2 3" | ./a.out
* OR
* ./a.out 1 2 3
*/

#include <stdio.h>
#include <string.h>

int main(int argc, char* argv[])
{
int fromstdin = 0;
int i = 1;
char infile[200];

if (argc == 1) fromstdin = 1;

if (fromstdin)
{
memset(infile, 0, 200);
while (scanf("%s", infile) != EOF)
{
printf("stdin : %s\n", infile);
}
}
else
{
i = 1;
while (argv[i] != NULL)
{
printf("input : %s\n", argv[i]);
i++;
}
}
return 0;
}

[jpollard]

A bug in there -

scanf("%s",infile)... is an obvious buffer overflow attack vector.

What happens if the input string is more than 200 bytes long...

It would also be easier to read if the program was in code blocks...

oh - the memset isn't really necessary. A null byte is put in the data from a %s handling. If you use other input methods then just setting the last byte to null would suffice, but that depends on how you read the data.

[RupertPupkin]

Your program gives different output based on how the input is quoted:

$ ./a.out a b "c d"
input : a
input : b
input : c d
$  echo a b "c d" | ./a.out
stdin : a
stdin : b
stdin : c
stdin : d
$ ./a.out 'a b "c d"'
input : a b "c d"
$ echo 'a b "c d"' | ./a.out
stdin : a
stdin : b
stdin : "c
stdin : d"

[jpollard]

Gives exactly what is called for.

Quoting is only done by the shell.

the list of parameters is as the shell provides them, and they are treated exactly the same way as lines of input.

Now, whether you want to use scanf is a different issue. Personally, I really really avoid using it. It does too much... and not enough. And that causes a lot of oddity. Some of what you are referring to is the "not enough". %s doesn't quite do what you think (it is NOT the same as a fgets which would read an entire line, but you have to make sure the trailing newline is removed; and handle any leftover data that is larger than the specified buffer)