Can someone explain me why this happens please? View as Markdown

This is per definition: In C local variables are not initialized with anything! The weird characters you see are content from prior memory usage leftover from calls to other functions. Its just garbage. In C, local variables must always be initialized.

Uwe Schindler
thetaphi@php.net - http://www.php.net
NSAPI SAPI developer
Bremen, Germany

-----Original Message-----
From: Chris Jiang [mailto:jiangcat@gmail.com]
Sent: Sunday, November 16, 2008 2:36 PM
To: internals@lists.php.net; "M. Karpelès"
Cc: internals@lists.php.net
Subject: Re: [PHP-DEV] Can someone explain me why this happens please?

Ah, greet appreciation! The memset() way works perfectly, but the res[0]
way didn't work.

Beside, I think you are right. Although I'm just a beginner in C
language, but from the experience of JS and PHP, also according to the
document I've been searching all the time, there should be something
related to time.h functions which might be more suitable for what I'm
doing. However, at the mean time, I'm just trying to get 'strings' to
work in C and Zend, hehe!

Still, this is a really strange experience. Where are those characters
come from? Shouldn't it be a clean array when I first created them?
Anything related to the zval structure?

Thank you again!

M. Karpelès wrote:

Hi,

Try initializing your "res" variable first.

either:

memset(&res, 0, sizeof(res));

Or:

res[0] = 0;

Both will work, it all depends if you want to write "clean" code, of
"fast" code (and your definition of both).

I believe there are cleaner way to do what you are doing, but I'll let
that to your curiosity.

Mark

Le dimanche 16 novembre 2008 à 21:15 +0800, Chris Jiang a écrit :

Hi all, since I started playing around with Zend API, I thought it
would
be better to start writing some small functions as practice. Then my
entire weekend became nightmare.

I've tried to add a function activated in dynamic module, and it gives
a
very strange result. This function is really simple: taking an integer
as argument, returns a 'hhhh:mm:ss' format string. If additional
argument (BOOL) is set to true, then the 'hhhh' will turn to 'DD hh'.

Now, it works fine while compiled with GCC alone in standard C style,
but while working as a PHP function, the result is like this:

(!靠备h2339:44:05
(!靠备窵▒97D 11:44:05

What are the characters in front of them? Where did they come? It's
really confusing......

The original Zend style code is as follow:

---

ZEND_FUNCTION(cj_format_clock)
{
char res[50], myb[10];
long mys = 0;
double myd, myh, mym;
zend_bool useDay = 0;

if ( zend_parse_parameters_ex(ZEND_PARSE_PARAMS_QUIET,
ZEND_NUM_ARGS()
TSRMLS_CC, "l|b", &mys, &useDay) == FAILURE )
{
php_error(E_ERROR, "Expecting
cj_format_clock([(INT)seconds])",
get_active_function_name(TSRMLS_C));
return;
}

if ( mys < 0 )
{
php_error(E_ERROR, "Number of second must be a possitive
integer",
get_active_function_name(TSRMLS_C));
return;
}

if ( useDay )
{
myd = mys / 86400;
mys %= 86400;
sprintf(myb, "%.0f", myd);
strcat(res, myb);
strcat(res, "D ");
}

myh = mys / 3600;
mys %= 3600;
if ( myh < 10 )
strcat(res, "0");
sprintf(myb, "%.0f", myh);
strcat(res, myb);

strcat(res, ":");

mym = mys / 60;
mys %= 60;
if ( mym < 10 )
strcat(res, "0");
sprintf(myb, "%.0f", mym);
strcat(res, myb);

strcat(res, ":");

if ( mys < 10 )
strcat(res, "0");
sprintf(myb, "%d", mys);
strcat(res, myb);

RETURN_STRING(res, 1);
}

Hi,

Try initializing your "res" variable first.

either:

memset(&res, 0, sizeof(res));

Or:

res[0] = 0;

Both will work, it all depends if you want to write "clean" code, of
"fast" code (and your definition of both).

I believe there are cleaner way to do what you are doing, but I'll let
that to your curiosity.

Mark

Le dimanche 16 novembre 2008 à 21:15 +0800, Chris Jiang a écrit :

Hi all, since I started playing around with Zend API, I thought it
would
be better to start writing some small functions as practice. Then my
entire weekend became nightmare.

I've tried to add a function activated in dynamic module, and it gives
a
very strange result. This function is really simple: taking an integer
as argument, returns a 'hhhh:mm:ss' format string. If additional
argument (BOOL) is set to true, then the 'hhhh' will turn to 'DD hh'.

Now, it works fine while compiled with GCC alone in standard C style,
but while working as a PHP function, the result is like this:

(!靠备h2339:44:05
(!靠备窵▒97D 11:44:05

What are the characters in front of them? Where did they come? It's
really confusing......

The original Zend style code is as follow:

---

ZEND_FUNCTION(cj_format_clock)
{
char res[50], myb[10];
long mys = 0;
double myd, myh, mym;
zend_bool useDay = 0;

if ( zend_parse_parameters_ex(ZEND_PARSE_PARAMS_QUIET,
ZEND_NUM_ARGS()
TSRMLS_CC, "l|b", &mys, &useDay) == FAILURE )
{
php_error(E_ERROR, "Expecting
cj_format_clock([(INT)seconds])",
get_active_function_name(TSRMLS_C));
return;
}

if ( mys < 0 )
{
php_error(E_ERROR, "Number of second must be a possitive
integer",
get_active_function_name(TSRMLS_C));
return;
}

if ( useDay )
{
myd = mys / 86400;
mys %= 86400;
sprintf(myb, "%.0f", myd);
strcat(res, myb);
strcat(res, "D ");
}

myh = mys / 3600;
mys %= 3600;
if ( myh < 10 )
strcat(res, "0");
sprintf(myb, "%.0f", myh);
strcat(res, myb);

strcat(res, ":");

mym = mys / 60;
mys %= 60;
if ( mym < 10 )
strcat(res, "0");
sprintf(myb, "%.0f", mym);
strcat(res, myb);

strcat(res, ":");

if ( mys < 10 )
strcat(res, "0");
sprintf(myb, "%d", mys);
strcat(res, myb);

RETURN_STRING(res, 1);
}

Le dimanche 16 novembre 2008 à 21:35 +0800, Chris Jiang a écrit :

Still, this is a really strange experience. Where are those characters
come from? Shouldn't it be a clean array when I first created them?
Anything related to the zval structure?

This is not PHP-related. When you define a variable, it has no
content, you have to initialize it. The characters you got are from the
uninitialized space you used in the stack.

C won't initialize variables for you as it would be a waste of time in
the case you already initialize it with a non-NULL value.

Anyway as this is not PHP-related, I suggest this discussion to be
continued outside of the PHP internals mailing list, if you have any
question, I can probably give you some pointers to good documentation,
just need to understand what you are trying to do.

Best regards,
Mark