Useful Function or Junk?

[James Brown]

Errmm...it's junk, sorry! You have problem with the way you calculate the size of the buffer: sizeof(szBuffer) will reduce to sizeof(char *) which is the size of a pointer - NOT the size of the buffer that it points to. So, you have to introduce a new parameter to specify the size at runtime. You might as well use ZeroMemory defined in windows.h which does this exact thing: VOID ZeroMemory(VOID *buf, SIZE_T length); And it's clearer what it does too :-) Regards, James
http://www.catch22.uk.net

[John Aldrich]

the reason why I have the function cast that way is because without the char * szBufferName convention, you woudl have to defin ethe size of the buffer within memset itself, when it's far simpler to just use the pointer and still get the same effect. It's good to see kids turning their minds to wholesum activities such as programming, instead of wasting their lives in the hedonistic disciplines of Sex, Drugs, & Rock & Roll... or Sex with Drugs, or Sex with Rocks while Rolling in Drugs, or whatever new-fangled perversions you little monsters have thought up now... [Shog9 on Kid Programmers]

[Ryan Johnston 0]

After reading a following post I went back and saw what you did. I think what you wanted was strlen(), but that only works for null terminated strings (Rarely what you are dealing with in the situation you described).

[Ryan Johnston 0]

What effect are you talking about? All your function does is sets the first 4 (in the case of 32bit pointers) bytes of your buffer to 0. sizeof(szBufferName) does not give you the size of the string pointed to by szBufferName, it gives you the size in bytes of the pointer itself.

[John Aldrich]

I used sizeof because theres no guarentee that your -going- to get a null terminated string, so i figured it made sense, at least on my level of understanding. It's good to see kids turning their minds to wholesum activities such as programming, instead of wasting their lives in the hedonistic disciplines of Sex, Drugs, & Rock & Roll... or Sex with Drugs, or Sex with Rocks while Rolling in Drugs, or whatever new-fangled perversions you little monsters have thought up now... [Shog9 on Kid Programmers]

[Ryan Johnston 0]

Well sizeof does not give you what you want.

[Todd Smith]

This only works if the buffer size is know at compile time. Works:

char buf[256];
memset(buf, 0, sizeof(buf));

This does NOT work:

Zero(char* buf)
{
memset(buf, 0, sizeof(buf));
}

main()
{
char buf[256];
Zero(buf);
}

Todd Smith

[Daniel Turini]

Is it a function for cleaning up 4-byte strings (Visual C++ assumed) ? Use ZeroMemory Win32 macro instead. Concussus surgo. When struck I rise.

[Daniel Turini]

Oh, almost forgot: you can do this (not my invention, this is a classic one): template class CWin32Struct : public T { public: CWin32Struct() { ZeroMemory(this, sizeof(T)); }; }; template class CWin32StructCB : public T { public: CWin32StructCB() { ZeroMemory(this, sizeof(T)); cb = sizeof(T); }; }; then use: CWin32Struct pi; or CWin32StructCB pmc;

[John Aldrich]

I'm sorry, but that's simply not correct. I've tested it both ways and it works if the array is defined as szSomeArray[17] = "testtesttesttest" or szSomeArray[] ="testtesttesttest". The effect is the same. It's good to see kids turning their minds to wholesum activities such as programming, instead of wasting their lives in the hedonistic disciplines of Sex, Drugs, & Rock & Roll... or Sex with Drugs, or Sex with Rocks while Rolling in Drugs, or whatever new-fangled perversions you little monsters have thought up now... [Shog9 on Kid Programmers]

[Daniel Turini]

That's because you are testing it the wrong way: printf(szSomeArray). Try printf(szSomeArray + 6) instead Concussus surgo. When struck I rise.

[Michael Dunn]

Just do it when you declare your array:

TCHAR szSomeString[14] = {0};

That zeros out the entire array. (Actually, it sets the first element in the array to 0 (the value specified) and then C initializes the remainder of the array to 0 (regardless of the value specified).) --Mike-- Just released - RightClick-Encrypt v1.3 - Adds fast & easy file encryption to Explorer My really out-of-date homepage Sonork-100.19012 Acid_Helm

[Christian Graus]

Personally, I never use char *, because I program C++ rather than C, and I never need the performance that would justify the clunkiness and error prone nature of char *. Apart from that, I agree with the person who said that if I needed to use something so ugly as a char*, I'd be too worried about efficiency to be adding the cost of a function call ( although it's concievable that the compiler would inline it ), and I would just call memset rather than add the cost of another function. It's one line vs. one line. Christian come on all you MS suckups, defend your sugar-daddy now. - Chris Losinger - 11/07/2002

[Todd Smith]

I just tested it and it failed. Without the right test you can't get the correct answer :)

void LiquidPlumber(char * szBufferName)
{
int size = sizeof(szBufferName);
memset(szBufferName, 0, size);
}

main()
{
char buf[256];
LiquidPlumber(buf);

char\* array = new char\[256\];
LiquidPlumber(array);

}

Step through and see what size is. Todd Smith

[John Aldrich]

Try this.

/////////////////////////////////////////////
//
// Liquid Plumber: Buffer Cleanup Function
//
// function takes 1 parameter which is the
// variable name of the char array to act on
// this is just a simple wrapper around the
// memset function to allow "hands-free" use
//
/////////////////////////////////////////////

void LiquidPlumber(char * szBufferName)
{
int size = sizeof(szBufferName);
memset(szBufferName, 0, size);
}

int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
char strDataToEncode[] = "testtesttesttest";

MessageBox(NULL, strDataToEncode, "Clogged Pipe", MB\_OK);

LiquidPlumber(strDataToEncode);

MessageBox(NULL, strDataToEncode, "Cleaned Pipe", MB\_OK);

return 0;

}

It's good to see kids turning their minds to wholesum activities such as programming, instead of wasting their lives in the hedonistic disciplines of Sex, Drugs, & Rock & Roll... or Sex with Drugs, or Sex with Rocks while Rolling in Drugs, or whatever new-fangled perversions you little monsters have thought up now... [Shog9 on Kid Programmers]

[Jim A Johnson]

Well, except for the fact that it doesn't work, has a non-descriptive name, has no error checking facilities.. no, it's not of much value. You don't work as a professional programmer I hope.

[Todd Smith]

Failed. Todd Smith

[Steve T]

Hi, You will very easiliy see where this goes wrong if you try to initialize your array to something other than zero, for example change it to 'A' and the result becomes "CLEANED PIPE" "AAAAtesttesttest" Steve T.

[Vagif Abilov]

It's very convenient to have a function that takes less arguments than memset. But since it does not do the job (note that sizeof(char*) is always 4 under Win32, no matter what is the length of the actual string), then you could skip the first argument as well: void OptimizedLiquidPlumber(void) { // Nothing to do, still almost as good as the original LiquidPlumber } ;P Vagif Abilov MCP (Visual C++) Oslo, Norway

[Todd Hoop]

Use the following and be done with it: *szBufferName = '\0'; I see code all the time when folks zero out strings for no reason. They waste processor time and their own. I had a friend who told me once that he worked with a contractor that zero'ed out every string by using a for-loop. Clever...