Help with Cast

afflictedd2 · 09-04-2008, 08:13 AM

Hi everyone,

I'm getting a warning when I try to do the (char *) cast on &buf, What is the correct cast for this?
The warning I get is : use of old-style cast

Thanks,
Ed.

Code:

        char buf[3][20];
	inline void readInRow() {
		currentData.clear();
		mIn.read((char *) &buf, sizeof(buf));
		for (int i=0; i < 3; ++i)
			currentData.push_back(string(buf[i]));
		printout(currentData);
		cout << endl;
	}

valaris · 09-04-2008, 08:19 AM

Why can't you just pass it buf? I also dont think you can cast an array to a pointer...but if you could i believe the syntax would be (char **) for 2-d arrays.

matsp · 09-04-2008, 08:31 AM

I think istream::read() expects a char *, but you probably don't want to use &buf, but rather buf. And since this is C++, you should use

Code:

mIn.read(reinterpret_cast<char *>(buf), sizeof(buf));

--
Mats

cpjust · 09-04-2008, 08:43 AM

Why not just pass buf[0] instead of forcing a 2D array to look like a 1D array?
Then you shouldn't need any casts.

afflictedd2 · 09-04-2008, 09:27 AM

Thanks matsp, that worked beautifully.

Quote:

Why not just pass buf[0] instead of forcing a 2D array to look like a 1D array?

Because with that matrix I want to represent 3 words of 20 characters max. I don't know how I would do that with a single array. I'm newbie sorry

Ed.

tabstop · 09-04-2008, 09:30 AM

You got it right here:

Code:

currentData.push_back(string(buf[i]));

It's the same idea.

matsp · 09-04-2008, 09:39 AM

Quote:

Originally Posted by afflictedd2

Thanks matsp, that worked beautifully.

Because with that matrix I want to represent 3 words of 20 characters max. I don't know how I would do that with a single array. I'm newbie sorry

Ed.

If you are reading strings from a text-file, then istream::read will not do the right thing for you - you'd have to loop and use getline or >> to read the individual words.

--
Mats

cpjust · 09-04-2008, 09:50 AM

Quote:

Originally Posted by afflictedd2

Thanks matsp, that worked beautifully.

Because with that matrix I want to represent 3 words of 20 characters max. I don't know how I would do that with a single array. I'm newbie sorry

Ed.

But then wouldn't this work?

Code:

for ( int x = 0; x < 3; ++x )
    mIn.read( buf[x], sizeof(buf[x]) );

afflictedd2 · 09-07-2008, 02:31 PM

Quote:

Originally Posted by matsp

If you are reading strings from a text-file, then istream::read will not do the right thing for you - you'd have to loop and use getline or >> to read the individual words.

--
Mats

It works. It's from a binary file not a text file.

matsp · 09-08-2008, 03:32 AM

Quote:

Originally Posted by afflictedd2

It works. It's from a binary file not a text file.

That's fine then - it's just that I've seen quite a few posts where someone is trying to read a text-file using read (or write it using write) and then complaining that the code doesn't work right - usually pointing at some completely different portion of code [such as the output or calculations]. I was just making sure that you are doing things the way they are meant to be done.

--
Mats

09-04-2008, 08:13 AM	#1
afflictedd2 Registered User Join Date: Jul 2008 Posts: 44	Hi everyone, I'm getting a warning when I try to do the (char ) cast on &buf, What is the correct cast for this? The warning I get is : use of old-style cast Thanks, Ed. Code: char buf[3][20]; inline void readInRow() { currentData.clear(); mIn.read((char ) &buf, sizeof(buf)); for (int i=0; i < 3; ++i) currentData.push_back(string(buf[i])); printout(currentData); cout << endl; }
afflictedd2 is offline

09-04-2008, 08:19 AM	#2
valaris Registered User Join Date: Jun 2008 Location: RING 0 Posts: 468	Why can't you just pass it buf? I also dont think you can cast an array to a pointer...but if you could i believe the syntax would be (char **) for 2-d arrays.
valaris is offline

09-04-2008, 08:31 AM	#3
matsp Kernel hacker Join Date: Jul 2007 Location: Farncombe, Surrey, England Posts: 15,686	I think istream::read() expects a char , but you probably don't want to use &buf, but rather buf. And since this is C++, you should use Code: mIn.read(reinterpret_cast<char >(buf), sizeof(buf)); -- Mats __________________ Compilers can produce warnings - make the compiler programmers happy: Use them! Please don't PM me for help - and no, I don't do help over instant messengers.
matsp is offline

09-04-2008, 08:43 AM	#4
cpjust and the hat of sweating Join Date: Aug 2007 Location: Toronto, ON Posts: 3,282	Why not just pass buf[0] instead of forcing a 2D array to look like a 1D array? Then you shouldn't need any casts.
cpjust is offline

09-04-2008, 09:30 AM	#6
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,836	You got it right here: Code: currentData.push_back(string(buf[i])); It's the same idea.
tabstop is online now

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