C / C++ / MFC

4-Aug-06 6:15

strToken is retaining an invalid value.
+ strToken 0xcccccccc <Bad Ptr> char *

unsigned int CSentenceAr::search(const char* strSearch)
{
// initialize local variables
unsigned long iWordCount = 0;
char buffer[MAX_SENTENCE_LENGTH] = {0};
/* Algorithm:

strToken shall initially contain the sentence string.
When strWord is found from the string, this is removed
from the string so that this function checks the rest of the
string for other instances of the word.
*/
char* strToken = {0};

for (int iCurrent = 0; iCurrent < Size; iCurrent++)
// copy to buffer, used as parameter for strstr.
{ memcpy(buffer, Sentences.strSentence[iCurrent], MAX_SENTENCE_LENGTH);
strToken = strstr(buffer,strSearch);

while (strToken !=0 && *strToken != 0)
{
if (strlen(strToken) > 0)
{ iWordCount++;
strToken += strlen(strSearch);
}

if (strToken >= buffer + MAX_SENTENCE_LENGTH)
{break;}
strToken = strstr(strToken, strSearch);
}
}
return (int) iWordCount;
}

Is it declared incorrectly?

Jon

David Crow4-Aug-06 6:32

4-Aug-06 6:32

jon_80 wrote:
strToken is retaining an invalid value.

At what point?

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

jon-804-Aug-06 6:53

4-Aug-06 6:53

Since it is declared (see the code), that's why I said retained. The problem is that since it has an invalid value the program is not going through the while loop.

Jon

David Crow4-Aug-06 7:16

4-Aug-06 7:16

strstr() will return NULL if strSearch is not found in buffer. That would be why the while loop is not entered. You should be able to set a breakpoint on the strstr() statement to confirm this.

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

jon-804-Aug-06 9:34

4-Aug-06 9:34

I meant to copy Sentences.strSentences to the buffer, look for the occurrence of strSearch within buffer and the pointer returned by strstr written to strToken.

memcpy(buffer, Sentences.strSentence[iCurrent], MAX_SENTENCE_LENGTH);
strToken = strstr(buffer,strSearch);

while (strToken !=0 && *strToken != 0)
{
if (strlen(strToken) > 0)
{ iWordCount++;

// The program looks for strSearch from the position where it was found onwards.

strToken += strlen(strSearch);
}

if (strToken >= buffer + MAX_SENTENCE_LENGTH)
{break;}
strToken = strstr(strToken, strSearch);
}

I hope it is clear now. What I don't get is what is wrong with strToken?

Jon

David Crow4-Aug-06 9:40

Re: bad pointer [modified]

4-Aug-06 9:40

jon_80 wrote:
strToken = strstr(buffer,strSearch);

What is the value of buffer and strSearch at this point?

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

Zac Howland4-Aug-06 6:57

Zac Howland

4-Aug-06 6:57

Break up the scope of your function:

Function 1 will take a single sentence and count how many times a substring appears in it.
Function 2 will take a collection of sentences and call Function 1 on each of them and sum the results.

const unsigned long MAX_SENTENCE_LENGTH = 100;

unsigned long HowManyInSentence(const char* sentence, const char* substring)
{
        char buffer[MAX_SENTENCE_LENGTH + 1] = {0};
        memcpy(buffer, sentence, MAX_WORD_LENGTH);
        char* token = 0;
        unsigned long wordCount = 0;
        token = strstr(buffer, substring);
        while (token != 0 && *token != 0)
        {
                if (strlen(token) > 0)
                {
                        ++wordCount;
                        token += strlen(substring);
                        if (token >= buffer + MAX_WORD_LENGTH)
                        {
                                break;
                        }
                }
                token = strstr(token, substring);
        }
        return wordCount;
}

unsigned long HowMany(const char* substring)
{
	// assume that g_sentences is declared somewhere and has MAX_SENTENCES entries
	unsigned long count = 0;
	for (int i = 0; i < MAX_SENTENCES; ++i)
	{
		count += HowManInSentence(g_sentences[i], substring);
	}

	return count;
}

Make sure that your buffer is null-terminated otherwise token will end up off in the weeds.

Oh, and token doesn't need to be assigned with scope (that is, you don't need char* token = {0};). char* token = 0; is fine and more readable.
-- modified at 12:58 Friday 4th August, 2006

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

jon-804-Aug-06 9:51

4-Aug-06 9:51

Thanks, but what do you mean by null-terminated? Also why this line of code?

if (token >= buffer + MAX_WORD_LENGTH) { break; }

Jon

David Crow4-Aug-06 9:56

4-Aug-06 9:56

jon_80 wrote:
...what do you mean by null-terminated?

Strings (not to be confused with an array of characters) in C must be nul-terminated in order to use string-related functions (e.g., strcpy(), strlen(), strstr(), strchr()).

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

Zac Howland4-Aug-06 10:05

Zac Howland

4-Aug-06 10:05

jon_80 wrote:
but what do you mean by null-terminated?

Lets say I write the following:

char* myString = "Hello, World!";

There are 13 characters in that string, but in memory, the size allocated for it would be 14. The reason is that the last character will be a 0, so the string actually looks like this in memory: Hello, World!\0. C-style strings require this, as do many C++ string wrappers.

if (token >= buffer + MAX_WORD_LENGTH)                        {                                
	break;
}

The above section of code checks to make sure that the token (which is nothing more than a character pointer) is not pointing to something that is outside the buffer. buffer is an array of characters (with a size of MAX_WORD_LENGTH -- which actually should have been renamed to MAX_SENTENCE_LENGTH). Basically, if token has moved passed the end of the string, we stop.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Stober4-Aug-06 8:19

Stober

4-Aug-06 8:19

>>memcpy(buffer, Sentences.strSentence[iCurrent], MAX_SENTENCE_LENGTH);

how is Sentences.strSentence declared? is it a char**? has memory been allocated or is your program just scribbling all over memory with that statement?

jon-804-Aug-06 9:29

using search in VC++ 2005 Pro

4-Aug-06 9:29

it's a char...

struct Sentence
{
char strSentence [MAX_LINES] [MAX_SENTENCE_LENGTH];
};

Jon

Stober4-Aug-06 4:39

Stober

4-Aug-06 4:39

When I select menu item Help-->Search, enter a search string, the IDE displays a URL in the middle of the screen and the only way I can get rid of it is to shut down and restart the entire IDE. This is really starting to pi$$ me off!

Any way to change that "feature"?

Sarath C4-Aug-06 5:35

Sarath C

4-Aug-06 5:35

Anyway I could not search from the net using MSDN installed with Visual Studio. it's saying that proxy authentication failed. even Im simply browsing using Internet explorer. what a heck is this Frown | :(

SaRath.

"Where I am from, there is no plan B. So, take advantage of today becuase tomorrow is not promised. - 50 Cent"

My Blog | Understanding State Pattern

Stober4-Aug-06 6:17

Stober

4-Aug-06 6:17

its probably the way you have your browser set up.

Sarath C4-Aug-06 6:53

Sarath C

4-Aug-06 6:53

there's no way in document explorer to explicitly set proxy. it's taking from internet explorer.
it's not asking for authentication.
however when im load a website in a new window inside the document explorer, it behaves as IE and works fine. but that credentials i have passed not taking in the search window Frown | :(

SaRath.

"Before you can learn to recognize what's wrong, you must learn to recognize what's right" - Raymond Chen."

My Blog | Understanding State Pattern