problem in mystring class

Code:

#include <iostream> #include <string> #include <cctype> using namespace std; class mystring : public string { public: mystring& lower_case(mystring& str=*this) { for (int i=0; i<str.size(); i++) { if (isupper(str[i])) { str[i] = tolower(str[i]); } } return str; } mystring& upper_case(mystring& str=*this) { for (int i=0; i<str.size(); i++) { if (islower(str[i])) { str[i] = toupper(str[i]); } } return str; } }; int main() { mystring str; while (true) { cout << "String: "; getline(cin, str, '\n'); if (str == "$") break; cout << "Upper case: " << str.upper_case(str) << endl; cout << "Lower case: " << str.lower_case(str) << endl; } return 0; }

if i give the value of *this as a default argument, i get following error on MSVC .Net 2003:

Code:

C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\ostream(574) : wa rning C4530: C++ exception handler used, but unwind semantics are not enabled. S pecify /EHsc C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\istream(828) : wa rning C4530: C++ exception handler used, but unwind semantics are not enabled. S pecify /EHsc C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\istream(1064) : w arning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc case.cpp(9) : error C2355: 'this' : can only be referenced inside non-static mem ber functions case.cpp(21) : error C2355: 'this' : can only be referenced inside non-static me mber functions

I'm sure default arguments are handled at the callers side, thus making "*this" being dereferenced outside the method where there is no class object.

You can't use "*this" before you are INSIDE the function.

What you could do is to use overloading, like this:

Code:

mystring& lower_case(mystring& str) { for (int i=0; i<str.size(); i++) { if (isupper(str[i])) { str[i] = tolower(str[i]); } } return str; } mystring& lower_case() // No argument - use "this" { return lower_case(*this); }

Edit: as the mystring& lower_case(mystring &str) doesn't touch "this", you could make it static.
--
Mats

Quote:

Originally Posted by Magos

I'm sure default arguments are handled at the callers side, thus making "*this" being dereferenced outside the method where there is no class object.

Spot on, and good explanation - I never explained why you can't use "this" as a default argument value.

--
Mats

I also see a big, fat warning that says exception handling is disabled in project settings... This is on by default, so you must have disabled it. Hopefully for a reason. Hopefully a good one.

No i did not do anything about exceptions at all!
I just compiled the program from command line like this:
cl case.cpp
I mostly use only command line, and i also don't understand what are those warnings about.

Do not compile using command lines.
Compile within the IDE. There's a reason the IDE can automatically compile for you and it's convenient and it's not error-prone.
Simply press F7 (if you've select C++ 6 settings).

Your current code will break and fold in so many ways because you aren't compiling correctly.
Again, use the IDE.

I'm really allergic to compiling stuff via the command line. It shouldn't be necessary.
Sheesh. You don't even know how to use the compiler properly and yet you compile using command-line interface.

that makes me ask for a little advice from you please help me here:

- i want MSVC to complete my symbol names, show completions etc. for all the files that are needed in my project.
what is the easiest way to do it?
- how do i compile my project using MSVC if i need to run a few custom tools over my source files and other files added to project.
also those tools produce some source files which need to be compiled. but they are generated by the tools.
how i set the MSVC to use these newly created files and compile them as well.

i tried to read about custom build steps, but was at lost. may be you can help me. by explaining in some easier steps.

ctrl-space gives you completion of the stuff you are typing. ctrl-shift-space (I think) gives the current parameters for function calls [etc].

--
Mats

Quote:

Originally Posted by manav

- i want MSVC to complete my symbol names, show completions etc. for all the files that are needed in my project.
what is the easiest way to do it?

It's typically called IntelliSense. MSVc's intellisense is a little poor, but doable. If you type a method, it will automatically show the parameters for those functions. If you need to force it to show it, mats listen the shortcuts. Typically, I just bind it to Alt+q, which is easier to use.
And you could also try Visual Assist X for Visual Studio. Very, very nice intellisense and other stuff plugin. Not free, but 30-days trial. And if you can reset the trial, all the better ;)

Quote:

- how do i compile my project using MSVC if i need to run a few custom tools over my source files and other files added to project.
also those tools produce some source files which need to be compiled. but they are generated by the tools.
how i set the MSVC to use these newly created files and compile them as well.

To this end, use the Custom Build Step in the project settings. Pre-build is executed before the compiler is called. Pre-link is called before the linker is called and post-build is called after the linker is finished.
If you need to compile extra source files, try to manually enter extra arguments to the compiler under the project settings.

those features work if i use MSVC for writing window specific code.
but i am writing code which does not use any windows api directly, i am using eg. Qt, boost and other portable
networking libraries. i also have their sources. now MSVC can find the definitions/declarations, can show completions, can do a lot of things.
how do i make it to do all those nice things for my Qt programs?

and if any body have done Qt they know that Qt source files need to run qmake do a little magic with the source files.
from command line its as simple as this:
qmake -project
qmake -makefile
nmake
how do i perform only these steps for my project build?
and also how do i make MSVC to do intellisense kinda stuff with Qt API?

Quote:

Originally Posted by manav

those features work if i use MSVC for writing window specific code.
but i am writing code which does not use any windows api directly, i am using eg. Qt, boost and other portable
networking libraries. i also have their sources. now MSVC can find the definitions/declarations, can show completions, can do a lot of things.
how do i make it to do all those nice things for my Qt programs?

and also how do i make MSVC to do intellisense kinda stuff with Qt API?

It will automatically parse and detect any headers you've included. So it should work with Qt, as well as your own source. You can also try deleting the intellisense database (the *.ncb file) in the project directory to see if it helps. No extra configuration should be necessary.
You can also try Visual Assist X.

Quote:

and if any body have done Qt they know that Qt source files need to run qmake do a little magic with the source files.
from command line its as simple as this:
qmake -project
qmake -makefile
nmake
how do i perform only these steps for my project build?

I have no idea what those command lines do or how they interact with your code, I can only guess. But Qt sounds like a pain. It shouldn't have to rely on command lines to build the darn thing. Just ship a little Dll or some other form of binary for the different platforms or provide instructions on how to create one such for each platform.

Qmake -project I suppose makes some changes to your project. That's fine. You can call that in the pre-build step.
Qmake -makefile makes a makefile for... qt only or your project? Does it create some library you need to link to?

Isn't it normally advised against inheriting from standard containers (due to the lack of virtual destructor) and wouldn't that also apply to std::string?

In this case, particularly since you apparently want to use the member function to provide the ability to convert other strings as well, wouldn't a much better approach be to provide a free function to_lower and to_upper for std::string (or download boost and use the ones that are already provided there)?

so just including the headers and specifying the include path in settings will work? i will try and post later.

about the qmake steps:
well they just make everything ready so just doing an nmake will make my programs.
how do i configure MSVC to just run nmake or use my makefile generated by qmake?

Oh and now that you mention it...
If the tolower/toupper functions are part of your class, they should perform the action on the object itself. When I call myobj.toupper(), I expect it to transform (or return a new object) with upper case.
If you want it to be able to mainpulate another object, making it static.

Quote:

Originally Posted by manav

so just including the headers and specifying the include path in settings will work? i will try and post later.

about the qmake steps:
well they just make everything ready so just doing an nmake will make my programs.
how do i configure MSVC to just run nmake or use my makefile generated by qmake?

You could call nmake in the pre-build stage, but I don't trust that makefile. I would rather find a solution that involves compiling Qt into a library and linking with that instead of messing with command lines and make files. It's only going to be a headache in the end.

well for the mystring function i will say:
i wanted to be able to pass a string obj to the function and made the *this default so it would work both ways. eg:

Code:

sting std_str = "ABC"; mystring str; //like this str.lower_case(std_str); //and on its own like this str.lower_case();

but i have changed my functions, they don't take any arguments now and modify *this and return it as well.

Bad. If you want a lower_case that can take another string object (which you really shouldn't need), make it static. This gives the effect that it's available in a namespace like mystring::lower_case and not part of the object itself.
To be better, you could create a namespace named String and put that function there instead.

Oh My GOD ! ! !
I Love You Elysia! Thanks a lot :)
The MSVC is doing all the completions etc. stuff with Qt API now :)
And for building I can still use the same old command line method (until I find a way with MSVC).

Quote:

Originally Posted by manav

And for building I can still use the same old command line method (until I find a way with MSVC).

I seriously recommend against it.
You are breaking lots of stuff in the code. If your code throws, it won't work as it should, for example (since you have disabled C++ exception handling!!). And who knows what else you've broken by compiling manually?
At least set up your project as it should compile and copy the command line from the GUI. At least do that. Microsoft's compiler is a complex beast that wasn't really meant to be used in CLI I bet, since they did it overly complex.

me too don't have any idea about good/bad command line options for cl but these are the options that i am using:

Code:

DEFINES = -DUNICODE -DQT_LARGEFILE_SUPPORT -DWIN32 -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT CFLAGS = -nologo -Zm200 -GS -Od -ZI -Gm -MDd -W3 $(DEFINES) CXXFLAGS = -nologo -Zm200 -GS -Od -ZI -Gm -MDd -GR -EHsc -W3 $(DEFINES)

i hope somebody who understands cl can tell how good/bad these options are!

EDIT: the above are for DEBUG mode.
here are RELEASE mode options:

Code:

DEFINES = -DUNICODE -DQT_LARGEFILE_SUPPORT -DWIN32 -DQT_DLL -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT CFLAGS = -nologo -Zm200 -GS -O1 -MD -DNDEBUG -W3 $(DEFINES) CXXFLAGS = -nologo -Zm200 -GS -O1 -MD -DNDEBUG -GR -EHsc -W3 $(DEFINES)

Huh? None of those are cl commands.
They all begin with "/" contrary to the linux standard of "-" which is really annoying rather than the "/" in my opinion.
And you aren't even using highest warning level, which is another reason you should avoid your manual compile alternative.

no tested it. cl understands options starting with the hyphen.

Sneaky Microsoft :p
Doesn't mention such a thing in the docs.

But do say, when it's multi-platform, they always introduce this unneccesary and stupid stuff. Using a makefile for compiling the project is stupid as you lose every functionality in the project settings.

EDIT:
Try this guide as well:
http://ldmartin68.com/QTSetup4VSNET.html
But ignore the advice about disabling precompiled headers.

Don't make the function static. Make it a free function as anon mentioned and don't derive from std::string at all. There's no reason to, it just creates unnecessary complexity. lower_case(my_str) is just as easy to call as my_str.lower_case().

Quote:

Originally Posted by Daved

Don't make the function static. Make it a free function as anon mentioned and don't derive from std::string at all. There's no reason to, it just creates unnecessary complexity. lower_case(my_str) is just as easy to call as my_str.lower_case().

Not to mention that it's actually more flexible: You can do my_str3 = lower_case(my_str1 + my_str2);

--
Mats

Well, I think you could do my_str3 = (my_str1 + my_str2).lower_case() too, but I don't really want to argue for that syntax.

Quote:

Originally Posted by Daved

Well, I think you could do my_str3 = (my_str1 + my_str2).lower_case() too, but I don't really want to argue for that syntax.

Ok, it's not something I would write, but I give you that it would be valid thing to do - but most people wouldn't even understand what it does...

Edit: It's when I see things like that, that I remember that I don't know C++ well enough - although I don't want to write code like that, I would at least want to know that it can be done... ;-)

--
Mats

Quote:

Originally Posted by matsp

Not to mention that it's actually more flexible: You can do my_str3 = lower_case(my_str1 + my_str2);

--
Mats

Obviously it might have its uses, but I don't recommend placing such a function inside the mystr class. It's not part of the class because it only modifies and returns the data from the argument, so it may well be placed outside the class and using public methods in the class for better encapsulation.
And what better place to put than inside a namespace such as String, where all your string functions are gathered?