Access Violation using memcmp?

This is a discussion on Access Violation using memcmp? within the C Programming forums, part of the General Programming Boards category; I get an access violation when I use memcmp... not too sure what that means, but heres the error: Unhandled ...

  1. #1
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    Access Violation using memcmp?

    I get an access violation when I use memcmp... not too sure what that means, but heres the error:

    Unhandled exception at 0x1024002d in myprogram.exe: 0xC0000005: Access violation reading location 0xffffffcc.
    Code:
    char * Compare(char *searchCmd)
    {
    	searchCmd = '\xA1';
    	while (memcmp(currentPlace, searchCmd, 1) != 0)
    		currentPlace++;
    }

  2. #2
    Chinese pâté foxman's Avatar
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    Your stuff is pretty weird. Doesn't make a lot of sense.


    Code:
    char * Compare(char *searchCmd)
    {
    	searchCmd = '\xA1';    // (char *) = (char); This looks highly suspicious
    
    	// I would like to know what's the value of currentPlace here, and would be curious to know his type
    	// Also, your loop might read in memory who doesn't belong to your program
    	while (memcmp(currentPlace, searchCmd, 1) != 0)
    		currentPlace++;
    
    	// Your function should return a (char *). Currently, it returns nothings.
    }
    What are you trying to do ?

  3. #3
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    Quote Originally Posted by foxman View Post
    Your stuff is pretty weird. Doesn't make a lot of sense.


    Code:
    char * Compare(char *searchCmd)
    {
    	searchCmd = '\xA1';    // (char *) = (char); This looks highly suspicious
    
    	// I would like to know what's the value of currentPlace here, and would be curious to know his type
    	// Also, your loop might read in memory who doesn't belong to your program
    	while (memcmp(currentPlace, searchCmd, 1) != 0)
    		currentPlace++;
    
    	// Your function should return a (char *). Currently, it returns nothings.
    }
    What are you trying to do ?
    well all im trying to do is read a byte from a global pointer to a char (called currentPlace) and seeing if it matches with the char searchCmd (so, basically seeing if the value of the byte what currentPlace is pointing to equals what the value of the byte that searchCmd points to)

    All currentPlace does is go up the memory values to see if any are equal to the value that searchCmd points to

  4. #4
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by someprogr View Post
    well all im trying to do is read a byte from a global pointer to a char (called currentPlace) and seeing if it matches with the char searchCmd (so, basically seeing if the value of the byte what currentPlace is pointing to equals what the value of the byte that searchCmd points to)

    All currentPlace does is go up the memory values to see if any are equal to the value that searchCmd points to
    That doesn't make sense, and doesn't explain why there would be a loop, or what '\xA1' is for. Virtually all of that code is utter garbage and of no use in any working program.
    Let me rephrase the question that has been asked:

    What is 'Compare' supposed to do, from the point of view of the code that calls it? Are you attempting to reimplement strcmp or strchr?
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