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Control Flow

2 (2.2%)

Arrays, Strings, Pointers, and References

8 (9%)

Functions

4 (4.5%)

Basic object-oriented programming

30 (33.7%)

A bit more advanced OOP (Composition, Operator overloading, Inheritance, Virtual Functions)

18 (20.2%)

Templates

8 (9%)

Other (Explain)

4 (4.5%)

Working with files?  (Streams)

15 (16.9%)

Total Members Voted: 89

[Blank Expression]

Dangerous assumptions there. sizeof(int) on your computer does not have to be the same as the computer that wrote the file. When dealing with file headers, always know the byte count of each data element and read that amount explicitly.

Edit: Would help to know the (hex) contents of the file.

Or just use the defined typedefs that say exactly how big something is. I want to punch a kitten whenever somebody uses "int". Every modern compiler includes stdint.h/cstdint. If you're going to be misusing C++, at least misuse it with the right tools.

[Shades]

Or just use the defined typedefs that say exactly how big something is. I want to punch a kitten whenever somebody uses "int". Every modern compiler includes stdint.h/cstdint.

Just to expand on that all the implementations of the standards have to support int8_t, int16_t, int32_t, uint8_t, uint16_t and uint32_t which are signed and unsigned 8, 16 and 32 bit values.

There is also a lot of other constants that are useful but those are the ones you'll use most commonly.

[olemars]

Only full implementations of C99. Visual Studio hasn't had a stdint.h in any versions prior to VS2010. Instead there are alternatives like __int8/16/32 and so on.

[Shades]

Only full implementations of C99. Visual Studio hasn't had a stdint.h in any versions prior to VS2010. Instead there are alternatives like __int8/16/32 and so on.

Unless they use boost which has an implementation of it, and why wouldn't they be using boost if they are working in c++?

Alternatively on visual studio 2005 or later you can use the files at http://code.google.com/p/msinttypes/ which is an implementation for visual studio. Of course if your using the free version of VS you may as well upgrade so you can abuse the cool functionality in the 2010 compiler.

[ILikePie]

Spoiler (click to show/hide)

Ok, now I'm using uint32_t instead, but that wasn't what was causing the problem.

What I'm trying to do is extract the image data out of a bitmap file. The starting at 10th byte of the file is an int (uint32_t) showing where the data starts (in this case, 54, or 0x36). The first fread reads this int and stores it in pos. Then I get the size of data by subtracting pos from the total file size (so size equals 16). The next  readf is supposed to read size amount of chars from the file, but instead it reads only 8.

Never mind, I forgot puts stops printing when it reaches a null character.

[Siquo]

Never mind, I forgot puts stops printing when it reaches a null character.

Hahaha, don't you love those "errors", where you only think something is wrong even if there isn't

[qwertyuiopas]

Doesn't windows.h (or some similar header) define a struct that corresponds to the header of a bitmap? I think they are BITMAPFILEHEADER and BITMAPINFOHEADER. Instead of reading by offset, then, you could directly read in the correct struct, then use the value that it contains. Bonus: There are more than one of those structs, so using one would make it easier to use others in turn.

[Blank Expression]

Only full implementations of C99. Visual Studio hasn't had a stdint.h in any versions prior to VS2010. Instead there are alternatives like __int8/16/32 and so on.

Good point, I forgot about that. As Shades noted, though, there are replacements.

(But, really, you can use the VS2010 compiler--which is a free download--with versions of VS as far back as VS2005, there's not much of a reason not to.)

[ILikePie]

Doesn't windows.h (or some similar header) define a struct that corresponds to the header of a bitmap? I think they are BITMAPFILEHEADER and BITMAPINFOHEADER. Instead of reading by offset, then, you could directly read in the correct struct, then use the value that it contains. Bonus: There are more than one of those structs, so using one would make it easier to use others in turn.

Microsoft has it on their site, and Wikipedia has nice documentation of bitmaps too.

[SolarShado]

Of course if your using the free version of VS you may as well upgrade so you can abuse the cool functionality in the 2010 compiler.

* SolarShado is interested

such as?

[olemars]

VS2010 has some C++0x support.

[TolyK]

C++0x is incl

VS2010 has some C++0x support.

Ninja'd.

[malimbar04]

Attempted to make a basic calculator, but for some reason it's giving me really strange answers. 23 * 45 gives an answer of 4.88005e-270 for example. Please help me debug... because I have no idea what it's doing wrong.

Spoiler (click to show/hide)

Code: [Select]

// Calculator.cpp

#include <iostream>
using namespace std;

// math functions
double add(double x, double y){
return x+y;}

double subtract(double x, double y){
return x+y;}

double multiply(double x, double y){
return x*y;}

double divide(double x, double y) {
return x/y;}

int main()
{
double num1;
double num2;
char mathFunction;
double solution;
 
// description
cout << "This is a basic math program." << endl;
cout << "It can add, subtract, multiply, or divide 2 numbers." << endl;
cout << "Which two numbers do you want to use?" << endl;

// numbers
cout << "First number: " << endl;
cin >> num1;
cout << "Second number: " << endl;
cin >> num2;

// converts mathFunction character into the correct function
cout << "Which function do you want to do? (options are + - * /)\n";
cin >> mathFunction;

switch (mathFunction)
{
case 1: '+';
solution = add(num1,num2);
cout << "answer = " << solution;
break;
case 2: '-';
solution = subtract(num1,num2);
cout << "answer = " << solution;
break;
case 3: '*';
solution = multiply (num1,num2);
cout << "answer = " << solution;
break;
case 4: '/';
solution = divide (num1,num2);
cout << "answer = " << solution;
break;
}

// recap and solution
cout << num1 << " " << mathFunction << " " << num2 << " = " << solution << endl;

return 0;
}

[Siquo]

Your switch. It is wrong.

you'll want
case '+':

instead of
case 1: '+';

Right now it skips those, and prints solution = 0, except that doubles and floats are often almost zero, so that's what you see.

[malimbar04]

ah, that makes more sense, thanks.

It also revealed an error that happened when I was changing the name of variables, I was attaching the solution to the final sentence, displaying something like 115 + 6 = 11. the 115 is just 11 attached to the real sentence of 5+6=11.

Sweetness.