Program crashes when trying to assign a value to a class variable

This is a discussion on Program crashes when trying to assign a value to a class variable within the C++ Programming forums, part of the General Programming Boards category; find.cpp Code: void find(vector<macros> &m, file &f) { char *c_file; c_file=new char[f.oldLength()]; f.oldFile().copy(c_file, f.oldLength()); for(int x=0;x<f.oldLength();x++) { if(c_file[x]=='#') { x++; ...

  1. #1
    Registered User
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    Dec 2009
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    Program crashes when trying to assign a value to a class variable

    find.cpp
    Code:
    void find(vector<macros> &m, file &f)
    {
        char *c_file;
        c_file=new char[f.oldLength()];
        f.oldFile().copy(c_file, f.oldLength());
        for(int x=0;x<f.oldLength();x++)
        {
            if(c_file[x]=='#')
            {
                x++;
                if(isValidMacro(c_file,x))
                {
                    x+=5;
                    f.addMacro();
                    m.push_back(macros());
                    m[f.numOfMacros()].atLoc(x);
                    m[f.numOfMacros()].toSymbol(getSymbol(c_file,x));
                }
            }
        }
    }
    
    string getSymbol(char *c_file, int &pos)
    {
        stringstream ss_symbol;
        string symbol;
        do
        {
            pos++;
        }while(c_file[pos]!=' ');
        do
        {
            ss_symbol<<c_file[pos];
            pos++;
        }while(c_file[pos]!='('&&c_file[pos]!=' ');
        ss_symbol>>symbol;
        return symbol;
    }
    macros.cpp (implementation file for the macros class, this function causes the crash)
    Code:
    void macros::toSymbol(string newSymbol)
    {
        pSymbol=newSymbol;
    }
    macros.h (class declaration)
    Code:
    class macros
    {
        public:
            macros();
            ~macros();
            void toSymbol(string newSymbol), toToken(string newToken), atLoc(int location);
    
            string symbol(), token(), args(int num);
            int numOfArgs(), loc();
        private:
            string pSymbol, pToken, *pArgs;
            int pNumOfArgs, pLocation;
    };
    Starting with the find() function, everything appears to work fine. The Code::Blocks debugger stopped working for me and I'm not quite as good at using gdb manually.. But I can tell it's the line pSymbol=newSymbol; that's causing the crash. I did some checking and similar functions in the macro class cause a crash during variable assignment. I have no idea what this is about.

    Thanks.

  2. #2
    CSharpener vart's Avatar
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    Rishon LeZion, Israel
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    1. why are you using char array instead of vector of chars?
    2. why are you using operator[] instead of at() to access your macros vector
    3. after first m.push_back(macros()); your vector contains 1 element I suppose. What is the value of f.numOfMacros() - is it zero at this time?
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  3. #3
    Registered User
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    Dec 2009
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    Quote Originally Posted by vart View Post
    1. why are you using char array instead of vector of chars?
    2. why are you using operator[] instead of at() to access your macros vector
    3. after first m.push_back(macros()); your vector contains 1 element I suppose. What is the value of f.numOfMacros() - is it zero at this time?

    1. Never thought of that but it's a good idea. I never had a problem with using pointers for dynamic arrays, so I always did that.
    2. Didn't know the at() function existed/was preferred.
    3. This is probably an issue, f.numOfMacros() would be returning 1 right now. That solved the problem, but I don't understand why it was crashing on the line in the class function instead of the line that tried to call the nonexistent part of the vector.

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