C / C++ / MFC

5-Apr-05 5:26

hiho@ll

i know this site is for windows programming, but i just wanted to know if my C-Code could have a problem, and this website is very well visited i think

for those who also use linux:
i'm coding on a suse linux box with kernel 2.4.21-226-default running gcc v 3.3.1

the problem is a function named strtok
which tokenizes my string using a delimiter
char test[]="hallo hallo2";
z.B. first call strtok(test," "); // returns hallo
seconde call strtok(NULL," "); // returns hallo2

this code works!:
char str[] ="This is a sample string,just testing.";
char * pch;
printf ("Splitting string \"%s\" in tokens:\n",str);
pch = strtok (str," ");
while (pch != NULL)
{
printf ("%s\n",pch);
pch = strtok (NULL, " ,.");
}

this code doesn't work! (i get a segmentation fault):
char *str ="This is a sample string,just testing."; // just changed char[]
char * pch;
printf ("Splitting string \"%s\" in tokens:\n",str);
pch = strtok (str," ");
while (pch != NULL)
{
printf ("%s\n",pch);
pch = strtok (NULL, " ,.");
}

could there a problem with the code itself?
what's the difference between pointers and arrays?
i thought there is no difference!

thx@ll

David Crow5-Apr-05 5:58

5-Apr-05 5:58

strtok() actually modifies the source string. That's why str[] works and str* does not.

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

ThinkingPrometheus5-Apr-05 6:06

5-Apr-05 6:06

?? 1. is there a difference?
char *str="hello";
str[0]='z';
--> str = "zello";

char str[]="hello";
str[0]='z';
--> str = "zello";

so what's the difference
and function header looks like this:
char *strtok(char *s, const char *delim);

2. str* doesn't work and str[] works! and not the other way, like u said

thx

David Crow5-Apr-05 6:19

5-Apr-05 6:19

ThinkingPrometheus wrote:
1. is there a difference?

Yes.

http://www.eskimo.com/~scs/C-faq/s6.html

ThinkingPrometheus wrote:
and function header looks like this:
char *strtok(char *s, const char *delim);

Since the first parameter is not const, that indicates it can/will be modified.

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

ThinkingPrometheus5-Apr-05 6:29

5-Apr-05 6:29

you wrote: strtok() actually modifies the source string. That's why str[] works and str* does not

look at my example prog!!!!
it works the other way!
str* doesn't work and str[] works! why?
thx

David Crow5-Apr-05 6:38

5-Apr-05 6:38

ThinkingPrometheus wrote:
you wrote: strtok() actually modifies the source string. That's why str[] works and str* does not

look at my example prog!!!!
it works the other way!

I think you need to re-read this thread. Your code indicates that char[] works but char* does not. Now you state that it works the other way.

The strtok() function works as it is intended to. Read its documentation. I provided you a link that explains the difference between a pointer and an array. Please read it.

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

ThinkingPrometheus5-Apr-05 6:42

5-Apr-05 6:42

i read the doc of strtok and your link

but it confuses me more than before

much more i'm asking why it doesn't work
cause strtok wants a pointer
i give it a pointer it makes segmentation fault
i give it an array it works!!!???

shouldn't it work if i give it a pointer and it wants a pointer!?
*confused*

Michael Dunn5-Apr-05 7:00

Michael Dunn

5-Apr-05 7:00

Because when you write:

char* s = "hello";

the compiler/linker may allocate read-only memory for that string, and set s to the address of that memory. Thus when you try and modify that string, it segfaults.

--Mike--
Visual C++ MVP Cool | :cool:

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David Crow5-Apr-05 7:03

5-Apr-05 7:03

ThinkingPrometheus wrote:
much more i'm asking why it doesn't work

Because it is not supposed to work. The statement char *p = "Hello" says that p is a pointer that points to a spot in memory that holds the string constant. Trying to change the contents of p[1] is illegal because is refers to a constant spot in memory. That spot in memory has no name.

The statement char p[] = "Hello" says that 6 bytes of memory is allocated for the string constant and that spot in memory is referred to as p.

In that link that I provided, read sections 6.2 and 6.4 very carefully. The difference is explained very well, and why they can't always be interchanged.

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

ThinkingPrometheus5-Apr-05 7:19

property sheets apply event

5-Apr-05 7:19

WOW

got it
that was the problem

thx to both of you

laiju5-Apr-05 4:07

Re: property sheets apply event

5-Apr-05 4:07

I would like to know if I can override any function such as OnApply() or OnOk() for a class derived from CPropertySheet.
The idea is i want to save some default settings property sheet whenever the user clicks apply /ok in a property sheet.

laiju

David Crow5-Apr-05 4:11

Re: property sheets apply event

5-Apr-05 4:11

laiju wrote:
I would like to know if I can override any function such as OnApply() or OnOk() for a class derived from CPropertySheet.

No, since neither method belongs to the CPropertySheet class. You can, however, override the virtual OnApply() and OnOK() methods that belong to the CPropertyPage class.

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

PJ Arends5-Apr-05 9:35

PJ Arends

5-Apr-05 9:35

Yes you can. Well, not technically "override" but you can catch the button clicks. CPropertySheet is a CWnd derived class so it has all the normal functionality of CWnd. It does receive BN_CLICKED commands from the buttons on the sheet, so you can add message handlers for the Ok and Apply buttons in you CPropertySheet derived class. Just be sure to implement the default behaviour by calling Default() in your handler.

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

"Obviously ??? You're definitely a superstar!!!" mYkel - 21 Jun '04

Within you lies the power for good - Use it!

Honoured as one of The Most Helpful Members of 2004

Hiding the default MDI Child

laiju5-Apr-05 3:58

5-Apr-05 3:58

I am using MDI architecture enable with Doc-View architecture.
Can anyone let me know if i can hide the first MDI child which comes by default.
I want to show that window later and not as soon as the application is started

laiju

YaronNir5-Apr-05 5:11

YaronNir

5-Apr-05 5:11

in the OnNewDocument in your Doc class, return FALSE and that is it

Ask not what your application can do for you,
Ask what you can do for your application

rgchezhian5-Apr-05 5:57

rgchezhian

5-Apr-05 5:57

Thanx for the response.
But if i set OnNewDocument to FALSE then i cant create new windows using file new option.isnt it?..Even if i set this to FALSE, at run time can i later set it TRUE sO that i can click New to launch MDI CHild windows later..
Thank you. .

laiju5-Apr-05 6:00

5-Apr-05 6:00

Thanx for the response.
But if i set OnNewDocument to FALSE then further i cant create new windows using file new option.isn't it?..Even if i set this to FALSE, at run time can i later set this option as TRUE so that i can click New to launch MDI CHild windows later..
Thank you. .

laiju

PJ Arends5-Apr-05 10:54

PJ Arends

5-Apr-05 10:54

In your app's InitInstance() function you will see the line

ParseCommandLine(cmdInfo)

Immediately after that line you have to check the value of cmdInfo.m_nShellCommand. If it is CCommandLineInfo::FileNew then the ProcessShellCommand(cmdInfo); line will open a new document. What you have to do is change the value of m_nShellCommand to CCommandLineInfo::FileNothing.

// Parse command line for standard shell commands, DDE, file open
CCommandLineInfo cmdInfo;
ParseCommandLine(cmdInfo);
 
// Disable the creation of a new document at startup
if (cmdInfo.m_nShellCommand == CCommandLineInfo::FileNew)
    cmdInfo.m_nShellCommand = CCommandLineInfo::FileNothing;
 
// Dispatch commands specified on the command line
if (!ProcessShellCommand(cmdInfo))
    return FALSE;

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

"Obviously ??? You're definitely a superstar!!!" mYkel - 21 Jun '04

Within you lies the power for good - Use it!

Honoured as one of The Most Helpful Members of 2004

laiju5-Apr-05 16:42