Putting variables into spawnl

[Satori]

#include <stdio.h>
#include <process.h>

int main()
{    
	char p[5] = "less";	/* pager */
	char buff[30];

	/* this shows test.txt in less */
	sprintf(buff, "\"%s\" \"test.txt\"", p);
	spawnlp(P_WAIT, "less", buff, NULL);
	
	/* this does NOT show test.txt in less */
	sprintf(buff, "\"%s\", \"%s\" \"test.txt\"", p, p);
	spawnlp(P_WAIT, buff, NULL);
	
	return 0;
}

I'm sure I must be missing something obvious, but how can I make the second example work properly?

Thanks in advance.

[Salem]

I wonder if your first one also shows "file not found" before going on to page your test.txt.
It seems broken, only less so than your 2nd attempt.

> but how can I make the second example work properly?
By realising that it's completely broken by design and just go with the first one.

This is it's prototype.

intptr_t _spawnlp(  
   int mode,  
   const char *cmdname,  
   const char *arg0,  
   const char *arg1,  
   ... const char *argn,  
   NULL   
);

spawn is NOT a command line parser that will break up space-separated commands.
That's YOUR task, so you can pass separate strings for each argn parameter.


You're literally trying to execute a program with the rather long name of
"less", "less" "test.txt"

I suppose you could pass the whole mess to cmd.exe, like
spawnlp(P_WAIT, "cmd.exe", buff, NULL);
and perhaps it'll eventually get around to doing what you want.

[Satori]

I wonder if your first one also shows "file not found" before going on to page your test.txt.

If it happens, it's gone too quickly to be noticed.

This is it's prototype.

intptr_t _spawnlp(  
   int mode,  
   const char *cmdname,  
   const char *arg0,  
   const char *arg1,  
   ... const char *argn,  
   NULL   
);

And, overlooked colon notwithstanding, that is what I thought I was doing; it's still broken.

Any suggestions?

Edit: to be clear, the value for "p" needs to be a variable (hence the title). Can spawnl not take variables, or am I just hamhanding it?

[Salem]

So long as your variables are char pointer or char array, spawn couldn't care less.

[Satori]

It works if I use a separate array for cmdname. I really can't imagine why I would need 2 sprintf's for one spawn though.

[Hodor]

It works if I use a separate array for cmdname. I really can't imagine why I would need 2 sprintf's for one spawn though.

Why isn't it as simple as:

#include <stdio.h>
#include <process.h>

int main()
{
    const char *cmd = "less";

    spawnlp(P_WAIT, cmd, cmd, "test.txt", NULL);

    return 0;
}

[Satori]

Because I have this tendency to make things more complicated than they need to be.

Thank you, that example helped a lot!

[Hodor]

Because I have this tendency to make things more complicated than they need to be.

Thank you, that example helped a lot!

No problem.

You understand why 'cmd' is given to spawnlp twice, right? Just in case you don't it's because by convention argv[0] is the name of the process/program. You could make the third argument to spawnlp something different but that wouldn't be how it's done by convention.

#include <stdio.h>
int main(int argc, char *argv[])
{
    printf("My process/program name is %s\n", argv[0]);
    return 0;
}