argv[0], etc

[Hal Styli]

hello,

Could someone tell me if the following code is standard C or am I being
naughty.
Essentially I want to point to the progam name by scanning along the
pathname pointed to by argv[0] but Im not sure if I can pass around the
'address' copied into myname in the manner shown. Are there scenarios /
implementations where accessing data pointed to by myname is not allowed?

Im a bit confused on pointer scope and afriad of memory access violations.

As a side issue is fname robust enough?

Thanks in advance.
Hal.

/*: 1:*/ /*showname*/
/*: 2:*/
/*: 3:*/ #include <stdio.h>
/*: 4:*/ #include <stdlib.h>
/*: 5:*/ #include <string.h>
/*: 6:*/
/*: 7:*/ #define PATHDELIM '\\'
/*: 8:*/
/*: 9:*/ char *myname;
/*:10:*/
/*:11:*/ #define PR(x) fprintf(stderr, #x " = %d\n", x)
/*:12:*/ #define PRS(x) fprintf(stderr, #x " = \"%s\"\n", x)
/*:13:*/
/*:14:*/ /*------------------------------------------------------------*/
/*:15:*/ char *fname(char *p)
/*:16:*/ {
/*:17:*/ /*similar to platform specific....
/*:18:*/ fnsplit(p, NULL, NULL, name, NULL)
/*:19:*/ and _splitpath(p, NULL, NULL, name, NULL)
/*:20:*/ ...but hopefully this is fully standard C?
/*:21:*/ */
/*:22:*/
/*:23:*/ char *q;
/*:24:*/
/*:25:*/ while(q=strchr(p,PATHDELIM))
/*:26:*/ p=q+1;
/*:27:*/
/*:28:*/ return p;
/*:29:*/ }
/*:30:*/ /*------------------------------------------------------------*/
/*:31:*/ void fred()
/*:32:*/ {
/*:33:*/ char *myname2;
/*:34:*/
/*:35:*/ PRS(myname); /* ok to use outside of main? */
/*:36:*/
/*:37:*/ myname2=myname;
/*:38:*/
/*:39:*/ PRS(myname2);
/*:40:*/ }
/*:41:*/ /*------------------------------------------------------------*/
/*:42:*/ int main(int argc, char *argv[] )
/*:43:*/ {
/*:44:*/ PR(argc); /* to avoid annoying warnings about not using argc*/
/*:45:*/
/*:46:*/ PRS(fname("no delimiter")); /* quick test 1*/
/*:47:*/ PRS(fname("")); /* quick test 2*/
/*:48:*/
/*:49:*/ myname= NULL;
/*:50:*/ PRS(myname); /* quick test 3*/
/*:51:*/
/*:52:*/ /* If argv[0] or fname(argv[0]) gives back nothing then I dont get
any output - fair enough */
/*:53:*/ PRS(fname(argv[0]));
/*:54:*/
/*:55:*/ myname=fname(argv[0]); /*meaningful to assign a global pointer to
one in main?*/
/*:56:*/
/*:57:*/ PRS(myname); /*should bomb on some systems?*/
/*:58:*/
/*:59:*/ fred();
/*:60:*/
/*:61:*/ return 0;
/*:62:*/ }
/*:63:*/ /*------------------------------------------------------------*/

 

[Hal Styli]

As a side issue is fname robust enough?

<<>>

Apparenlty not!

/*:49:*/ myname= NULL;
/*:50:*/ PRS(myname); /* quick test 3*/

should have been:

/*:49:*/ myname= NULL;
/*:50:*/ PRS(fname(myname)); /* quick test 3*/

which bombs on Borland, presumably everywhere else too!

 

[Derk Gwen]

# Essentially I want to point to the progam name by scanning along the
# pathname pointed to by argv[0] but Im not sure if I can pass around the

You need to verify your system doesn't set argv[0] to 0.

Also for systems like unix, the exec functions allows the executable file and
argv[0] to be completely unrelated.

 

[Hal Styli]

You need to verify your system doesn't set argv[0] to 0.

doesnt making the change: /*:24:*/ if(!p) return p;
catch this ?

 

[Mark McIntyre]

hello,

Could someone tell me if the following code is standard C or am I being
naughty.

/*:10:*/
/*:11:*/ #define PR(x) fprintf(stderr, #x " = %d\n", x)
/*:12:*/ #define PRS(x) fprintf(stderr, #x " = \"%s\"\n", x)

yuck. Get rid of the BASIC style line numbering, and the pointless
macros, and then repost. This is unreadable. If your editor can't
tell you which line is which, get a better editor.....

 

[Hal Styli]

yuck. Get rid of the BASIC style line numbering, and the pointless

macros, and then repost. This is unreadable. If your editor can't
tell you which line is which, get a better editor.....

The intention was to cut down on reposts which are more painful in my view.
The macro is effectively a so here goes....

/*showname*/

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

#define PATHDELIM '\\'

char *myname;

/*------------------------------------------------------------*/
char *fname(char *p)
{
/*similar to platform specific....
fnsplit(p, NULL, NULL, name, NULL)
and _splitpath(p, NULL, NULL, name, NULL)
...but hopefully this is fully portable/ANSI/etc?
*/

char *q;

if(!p)
return p;

while(q=strchr(p,PATHDELIM))
p=q+1;

return p;
}
/*------------------------------------------------------------*/
void fred()
{
char *myname2;

puts(myname); /* ok to use outside of main? */

myname2=myname;

puts(myname2);
}
/*------------------------------------------------------------*/
int main(int argc, char **argv )
{
/* to avoid annoying warnings about not using argc*/
printf("argc=%d\n", argc);

puts(fname("no delimiter")); /* quick test 1*/
puts(fname("")); /* quick test 2*/

myname= NULL;
puts(fname(myname)); /* quick test 3*/

puts(fname(argv[0]));

myname=fname(argv[0]);

puts(myname);

fred();

return 0;
}
/*------------------------------------------------------------*/

 

[Hal Styli]

The macro is effectively a so here goes....

a 'puts'!

 

[Mark McIntyre]

The intention was to cut down on reposts which are more painful in my view.
The macro is effectively a so here goes....
(snippage)
char *q;

if(!p)
return p;

Just return NULL here... same difference, gives the compiler less to
do.

(snippage)

puts(myname); /* ok to use outside of main? */

yes, its a file-scope variable.

myname= NULL;
puts(fname(myname)); /* quick test 3*/

this is not allowed - you can't pass NULL to puts, its not a string.
You could pass an empty string tho.