Odd char string initialization in structs

[gustavo]

I was looking at the Sendmail's source code, and i've got confused
about this kind of initialization:

------------------------
struct prival PrivacyValues[] =
{
{ "public", PRIV_PUBLIC },
{ "needmailhe lo", PRIV_NEEDMAILHE LO },
{ "needexpnhe lo", PRIV_NEEDEXPNHE LO },
{ "needvrfyhe lo", PRIV_NEEDVRFYHE LO },
....
};
------------------------

I'm familiar with char string[] = "foo", but i have no idea what the
above snip of code is doing. Anyone could please explain?

[ciju]

gustavo wrote:

I was looking at the Sendmail's source code, and i've got confused
about this kind of initialization:

------------------------
struct prival PrivacyValues[] =
{
{ "public", PRIV_PUBLIC },
{ "needmailhe lo", PRIV_NEEDMAILHE LO },
{ "needexpnhe lo", PRIV_NEEDEXPNHE LO },
{ "needvrfyhe lo", PRIV_NEEDVRFYHE LO },
...
};
------------------------

I'm familiar with char string[] = "foo", but i have no idea what the
above snip of code is doing. Anyone could please explain?

It is just the initialization of an array of structure.
It can be done in another way in your code.

Eg:
PrivayValues[0].field1 = "public";
PrivayValues[0].field2 = PRIV_PUBLIC;

PrivayValues[1].field1 = "needmailhe lo";
PrivayValues[1].field2 = PRIV_NEEDMAILHE LO;

-----
PrivayValues[n].field1 = "--";
PrivayValues[n].field2 = --;

[Kishore Yada]

can you also provide what is struct prival..

I suppose it must be

struct prival
{
char *x;
int y;
};
In the above case,
one element of the struct can be created using

struct prival OneElement = { "anystring" , ANY_INTEGER };

The first member might be confusing. What it does is
1. Stores "anystring" into the string table.
2. Puts a pointer in OneElement.x

In a C program whereever string constants occur, they are replaced by
pointers and the string constants are moved to the string table.

But, array initialization is an exception to that.

when we write string[] = "foo",
the compiler actually takes it as

string[4] = { 'f', 'o', 'o' , '\0' };

and therefore "foo" does not go to the string table at all.
Regards,
Yada Kishore

[slebetman]

gustavo wrote:

I was looking at the Sendmail's source code, and i've got confused
about this kind of initialization:

------------------------
struct prival PrivacyValues[] =
{
{ "public", PRIV_PUBLIC },
{ "needmailhe lo", PRIV_NEEDMAILHE LO },
{ "needexpnhe lo", PRIV_NEEDEXPNHE LO },
{ "needvrfyhe lo", PRIV_NEEDVRFYHE LO },
...
};
------------------------

I'm familiar with char string[] = "foo", but i have no idea what the
above snip of code is doing. Anyone could please explain?

char string[] = "foo";

is actually just a convenient shortcut of the more general form:

char string[] = {
'f' ,
'o' ,
'o' ,
'\0'
};

The general form applies to all types in C, for example:

int example[] = {
100,
200,
300
};

this includes structs, for example:

struct thing {
char *name;
int size;
};

struct thing stuff[] = {
{"Me", 100},
{"Myself", 200},
{"I", 300}
};

[ais523]

gustavo wrote:

I was looking at the Sendmail's source code, and i've got confused
about this kind of initialization:

------------------------
struct prival PrivacyValues[] =
{
{ "public", PRIV_PUBLIC },
{ "needmailhe lo", PRIV_NEEDMAILHE LO },
{ "needexpnhe lo", PRIV_NEEDEXPNHE LO },
{ "needvrfyhe lo", PRIV_NEEDVRFYHE LO },
...
};
------------------------

I'm familiar with char string[] = "foo", but i have no idea what the
above snip of code is doing. Anyone could please explain?

[The quote above is to identify the thread]

After reading the responses to this thread, I started wondering whether
the 'universal initialiser' {0} could apply to types like int which can
be initialised normally. So I wrote the program

#include <stdio.h>

int i = {0};
int j = {1};

int main(void)
{
printf("%d %d\n",i,j);
return 0;
}

which compiles on c89-conforming gcc with warnings turned up to the max
with no diagnostics, printing
0 1
as expected. Is it really possible to initialise anything like this?

[Flash Gordon]

ais523 wrote:

<snip>

After reading the responses to this thread, I started wondering whether
the 'universal initialiser' {0} could apply to types like int which can
be initialised normally. So I wrote the program

#include <stdio.h>

int i = {0};
int j = {1};

int main(void)
{
printf("%d %d\n",i,j);
return 0;
}

which compiles on c89-conforming gcc with warnings turned up to the max
with no diagnostics, printing
0 1
as expected. Is it really possible to initialise anything like this?

Yes, this is perfectly legal C and is defined as doing what you expect.
--
Flash Gordon, living in interesting times.
Web site - http://home.flash-gordon.me.uk/
comp.lang.c posting guidelines and intro:
http://clc-wiki.net/wiki/Intro_to_clc

Inviato da X-Privat.Org - Registrazione gratuita http://www.x-privat.org/join.php

[edware]

Flash Gordon wrote:

ais523 wrote:

<snip>

After reading the responses to this thread, I started wondering whether
the 'universal initialiser' {0} could apply to types like int which can
be initialised normally. So I wrote the program

#include <stdio.h>

int i = {0};
int j = {1};

int main(void)
{
printf("%d %d\n",i,j);
return 0;
}

which compiles on c89-conforming gcc with warnings turned up to the max
with no diagnostics, printing
0 1
as expected. Is it really possible to initialise anything like this?

Yes, this is perfectly legal C and is defined as doing what you expect.

struct test_t {
char *a;
int b;
double c;
};

int main(void)
{
struct test_t test = { 0 };
}

Will this initialization set the whole struct to 0,
or just the first member, byte, or something like that?

[Default User]

ciju wrote:

gustavo wrote:

I was looking at the Sendmail's source code, and i've got confused
about this kind of initialization:

------------------------
struct prival PrivacyValues[] =
{
{ "public", PRIV_PUBLIC },
{ "needmailhe lo", PRIV_NEEDMAILHE LO },
{ "needexpnhe lo", PRIV_NEEDEXPNHE LO },
{ "needvrfyhe lo", PRIV_NEEDVRFYHE LO },
...
};
------------------------

I'm familiar with char string[] = "foo", but i have no idea what the
above snip of code is doing. Anyone could please explain?

It is just the initialization of an array of structure.
It can be done in another way in your code.

Eg:
PrivayValues[0].field1 = "public";
PrivayValues[0].field2 = PRIV_PUBLIC;

This is not the same thing at all. You have assignment, not
initialization. If field1 happens to be an array of char rather than a
pointer to char, your version would be illegal.

Similarly, if either field1 or field2 happened to be const.


Brian

[Flash Gordon]

edware wrote:

<snip>

struct test_t {
char *a;
int b;
double c;
};

int main(void)
{
struct test_t test = { 0 };
}

Will this initialization set the whole struct to 0,
or just the first member, byte, or something like that?

It will initialise the entire struct so appropriate 0 type values (null
pointers, 0, 0.0 as appropriate). If you initialise any of it to any
value then the rest gets initialised to an appropriate 0 value for the type.
--
Flash Gordon, living in interesting times.
Web site - http://home.flash-gordon.me.uk/
comp.lang.c posting guidelines and intro:
http://clc-wiki.net/wiki/Intro_to_clc

Inviato da X-Privat.Org - Registrazione gratuita http://www.x-privat.org/join.php

[CBFalconer]

Flash Gordon wrote:

edware wrote:

<snip>

struct test_t {
char *a;
int b;
double c;
};

int main(void)
{
struct test_t test = { 0 };
}

Will this initialization set the whole struct to 0,
or just the first member, byte, or something like that?

It will initialise the entire struct so appropriate 0 type values
(null pointers, 0, 0.0 as appropriate). If you initialise any of
it to any value then the rest gets initialised to an appropriate
0 value for the type.

NOT to null pointers. Those you have to handle yourself.

--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell. org/google/>
Also see <http://www.safalra.com/special/googlegroupsrep ly/>