bad pointer

[David Crow]

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 80]

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

[Zac Howland]

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

[David Crow]

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

[Stober]

>>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 80]

:) it's a char... struct Sentence { char strSentence [MAX_LINES] [MAX_SENTENCE_LENGTH]; }; Jon

[jon 80]

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 Crow]

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

[jon 80]

Thanks, but what do you mean by null-terminated? Also why this line of code? if (token >= buffer + MAX_WORD_LENGTH) { break; } Jon

[David Crow]

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 Howland]

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