Exercise 5-14

[mdh]

I have Tondo and Gimpel. There are a couple of aspects of their
answer that puzzles me.

The Question is to modify a sort program to handle a -r flag
( function is irrelevant), which needs to wrok together with a -n flag
( function again irrelevant..I believe).

Firstly, a very brief outline of the function.

......numerous function declarations;

#define NUMERIC 1

static char option = 0;
main (int argc, char *argv[])
{

.....snip....
while ( --argc 0 && (*++argv)[0] == '-')
...snip...

switch (c){

case 'n':

option |= NUMERIC;

....snip...
}
My first question relates to the use of the qualifyer "static";

My understanding ( or lack of) is that a static variable outside of a
function limits the scope of that variable to that file. Is this just
good programming by T&G or is there another good reason for this?

Secondly, is this use of bitwise operators commonly used to set and
get flags in a program in C?

Thanks in advance.

[rahul]

On Jul 14, 8:56*am, mdh <[e-mail]:

My understanding ( or lack of) is that a static variable outside of a
function limits the scope of that variable to that *file. Is this just
good programming by T&G or is there another good reason for this?

Statics has got internal linkage. They won't be visible outside this
file. If some other object code you link with has got an identifier
called option, collision/shadowing won't happen as option is static.
It is considered a good programming practice to declare variables and
function as static if you intend to use them just in the given file.
Also, static data is initialized and won't contain garbage value. It
does not make a difference as it has been explicitly declared to be 0.
It is again a good practice to explicitly initialize static and global
variables.

Secondly, is this use of bitwise operators commonly used to set and
get flags in a program in C?

It more or less depends on your style. But yes, it does seem very
common in POSIX API(probably even Win32 API, but I have not used much
of that).

[mdh]

On Jul 13, 9:42*pm, rahul <[e-mail]:

On Jul 14, 8:56*am, mdh <[e-mail]:

My understanding ( or lack of) is that a static variable outside of a
function limits the scope of that variable to that *file. Is this just
good programming by T&G or is there another good reason for this?

Statics has got internal linkage. They won't be visible outside this
file. If some other object code *you link with has got an identifier
called option, collision/shadowing won't happen as option is static.
It is considered a good programming practice to declare variables and
function as static if you intend to use them just in the given file.
Also, static data is initialized and won't contain garbage value. It
does not make a difference as it has been explicitly declared to be 0.
It is again a good practice to explicitly initialize static and global
variables.

Secondly, is this use of bitwise operators commonly used to set and
get flags in a program in C?

It more or less depends on your style. But yes, it does seem very
common in POSIX API(probably even Win32 API, but I have not used much
of that).

Thanks Rahul. Just wanted to make sure.

[santosh]

mdh wrote:

I have Tondo and Gimpel. There are a couple of aspects of their
answer that puzzles me.

The Question is to modify a sort program to handle a -r flag
( function is irrelevant), which needs to wrok together with a -n flag
( function again irrelevant..I believe).

Firstly, a very brief outline of the function.

.....numerous function declarations;

#define NUMERIC 1

static char option = 0;
main (int argc, char *argv[])
{

....snip....
while ( --argc 0 && (*++argv)[0] == '-')
...snip...

switch (c){

case 'n':

option |= NUMERIC;

...snip...
}
My first question relates to the use of the qualifyer "static";

My understanding ( or lack of) is that a static variable outside of a
function limits the scope of that variable to that file. Is this just
good programming by T&G or is there another good reason for this?

The static qualifier can be used on both functions and objects and with
both functions and external objects it limits their visibility to the
rest of that translation unit. It's commonly used for this purpose to
mitigate excessive namespace pollution.

Secondly, is this use of bitwise operators commonly used to set and
get flags in a program in C?

Very much so. This is usually more easier than using bitfields though a
beginner may find manipulating the latter more intuitive.

PS. Note that uninitialised static objects are automatically initialised
to zero, but it's good practise to explicitly initialise them anyway.

[mdh]

On Jul 13, 10:52*pm, santosh <[e-mail]:

mdh wrote:

I have Tondo and Gimpel. There are a couple of *aspects of their
answer that puzzles me.

The Question *is to modify a sort program to handle a -r flag
( function is irrelevant), which needs to wrok together with a -n flag
( function again irrelevant..I believe).

Firstly, a very brief outline of the function.

.....numerous function declarations;

#define NUMERIC 1

static char option = 0;

main (int argc, char *argv[])
{

....snip....

while ( --argc 0 && (*++argv)[0] == '-')
*...snip...

switch (c){

case 'n':

option |= NUMERIC;

...snip...

}

My first question relates to the use of the qualifyer "static";

My understanding ( or lack of) is that a static variable outside of a
function limits the scope of that variable to that *file. Is this just
good programming by T&G or is there another good reason for this?

The static qualifier can be used on both functions and objects and with
both functions and external objects it limits their visibility to the
rest of that translation unit. It's commonly used for this purpose to
mitigate excessive namespace pollution.

Secondly, is this use of bitwise operators commonly used to set and
get flags in a program in C?

Very much so. This is usually more easier than using bitfields though a
beginner may find manipulating the latter more intuitive.

PS. Note that uninitialised static objects are automatically initialised
to zero, but it's good practise to explicitly initialise them anyway.

Thanks Santosh