49423, January 2001

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Frequently Asked Questions

Question

When I move my C++ source between the gbar/unix and my pc/windows I have problems with line-shifts.

Answer

Unix and windows/DOS represent line-shifts in different ways. To avoid problems you should always keep your files in unix format. 

Emacs can use several different coding systems. To save your text-file in unix format, while you are editing the file execute the command 

C-x <RET> f CODING <RET>'

where the CODING for instance could  be 'raw-text-unix'. The text file will now be in unix format (and the characters to the left in the mode line will change to  -(Unix)%% ). The file will be in unix format also when you later open it again in Emacs. 

Read about CODING in Emacs menu: Help/Manuals/Browse Manual with Info/Emacs/(Coding Systems|Specify Coding| ...)

 

Question

My WExpressionShop program sometimes writes curious characters in numbers, something like this

(x + 3.4a¸±a + y) * (x + 3.4a€²a + y)

I have used the proposed method from the available C++ files (for the Val class):

#include <strstream>
.........
{
    ostrstream os; os<<theVal.NumVal;
    return string(os.str());
}

What is wrong?

Answer

The program does not work on all platforms (sorry). os.str() gives a pointer to a string not necessarily terminated by a null-character. The program above should be changed to

{
    ostrstream os; os << theVal.NumVal << '\0';
    return string(os.str());
}

A more complicated solution is shown on the slide #3 in the slide set about Symbolic Expression:

{ 
    string res; char* p;
    ostrstream os; os << theVal.NumVal; p= os.str();
    for(int i=0;i<os.pcount();i++){res+= p[i];}
    return res;
}

The double to string conversion could be done in a simpler way by using the library <sstream> and the ostringstream class, but as far as I can see that library has not yet been implemented in the gcc 2.95.2 compiler.

 

 

Hans Bruun ( hab@imm.dtu.dk ) 21.06.01