Segmentation fault driven of a null reference in a c++ header file

Question

Can anyone find out what is wrong with the following part of code:

private:
     TUcdFileReader& operator = (const TUcdFileReader& r) { Fail; return *((TUcdFileReader *) 0); }
     TUcdFileReader(const TUcdFileReader& r) { Fail; }

This belongs to a header file in a c library (SNAP) which I use in my code. When I compile my code in a linux based system, the below warning shows up:

Snap-2.1/glib-core/unicode.h(1678): warning #327: NULL reference is not allowed
                TUcdFileReader& operator = (const TUcdFileReader& r) { Fail; return *((TUcdFileReader *) 0); }

Which in overall lead me to a segmentation fault as follows: (and I suspect it is because of the above warning)

WARNING: Job died due to SIGSEGV - Invalid memory reference

I dont write the whole header file since it is long and makes confusion, but it is the address of it: http://snap.stanford.edu/snap/doc/snapuser-ref/dd/d90/unicode_8h_source.html Here I wrote the bigger part of header file that uses TUcdFileReader:

protected:

class TUcdFileReader
{
protected:
    TChA buf;
public:
    TChA comment; // contains '#' and everything after it
protected:
    FILE *f;
    int putBackCh;
    int GetCh() {
        if (putBackCh >= 0) { int c = putBackCh; putBackCh = EOF; return c; }
        return fgetc(f); }
    void PutBack(int c) { Assert(putBackCh == EOF); putBackCh = c; }
    // Returns 'false' iff the EOF was encountered before anything was read.
    bool ReadNextLine() {
        buf.Clr(); comment.Clr();
        bool inComment = false, first = true;
        while (true) {
            int c = GetCh();
            if (c == EOF) return ! first;
            else if (c == 13) {
                c = GetCh(); if (c != 10) PutBack(c);
                return true; }
            else if (c == 10) return true;
            else if (c == '#') inComment = true;
            if (! inComment) buf += char(c);
            else comment += char(c); }
            /*first = false;*/}
private:
    TUcdFileReader& operator = (const TUcdFileReader& r) { Fail; return *((TUcdFileReader *) 0); }
    TUcdFileReader(const TUcdFileReader& r) { Fail; }
public:
    TUcdFileReader() : f(0) { }
    TUcdFileReader(const TStr& fileName) : f(0), putBackCh(EOF) { Open(fileName); }
    void Open(const TStr& fileName) { Close(); f = fopen(fileName.CStr(), "rt"); IAssertR(f, fileName); putBackCh = EOF; }
    void Close() { putBackCh = EOF; if (f) { fclose(f); f = 0; }}
    ~TUcdFileReader() { Close(); }
    bool GetNextLine(TStrV& dest) {
        dest.Clr();
        while (true) {
            if (! ReadNextLine()) return false;
            TStr line = buf; line.ToTrunc();
            if (line.Len() <= 0) continue;
            line.SplitOnAllCh(';', dest, false);
            for (int i = 0; i < dest.Len(); i++) dest[i].ToTrunc();
            return true; }}
    static int ParseCodePoint(const TStr& s) {
        int c; bool ok = s.IsHexInt(true, 0, 0x10ffff, c); IAssertR(ok, s); return c; }
    static void ParseCodePointList(const TStr& s, TIntV& dest, bool ClrDestP = true) { // space-separated list
        if (ClrDestP) dest.Clr();
        TStrV parts; s.SplitOnWs(parts);
        for (int i = 0; i < parts.Len(); i++) {
            int c; bool ok = parts[i].IsHexInt(true, 0, 0x10ffff, c); IAssertR(ok, s);
            dest.Add(c); } }
    static void ParseCodePointRange(const TStr& s, int& from, int &to) { // xxxx or xxxx..yyyy
        int i = s.SearchStr(".."); if (i < 0) { from = ParseCodePoint(s); to = from; return; }
        from = ParseCodePoint(s.GetSubStr(0, i - 1));
        to = ParseCodePoint(s.GetSubStr(i + 2, s.Len() - 1)); }
};

Further, the only place that TUcdFileReader is called :

class TSubcatHelper
    {
    public:
        bool hasCat; TUniChSubCategory subCat;
        TStrH invalidCatCodes;
        TUniChDb &owner;

        TSubcatHelper(TUniChDb &owner_) : owner(owner_) { }

        void ProcessComment(TUniChDb::TUcdFileReader &reader)
        {
....

http://stackoverflow.com/questions/6716091/assigning-a-reference-by-dereferencing-a-null-pointer — selalerer, Feb 15 '14 at 06:38

score 0 · Accepted Answer · answered Feb 15 '14 at 06:40

0

The class TUcdFileReader is specifically defined as NOT having assignment or copy constructors, i.e.

private:
    TUcdFileReader& operator = (const TUcdFileReader& r) 
               { Fail; return *((TUcdFileReader *) 0); }
    TUcdFileReader(const TUcdFileReader& r) { Fail; }

looks like they are meant to fail.

Somewhere in the code they are being called - if you replacing those with:

private:
    TUcdFileReader& operator = (const TUcdFileReader& r); //**not implemented** 
    TUcdFileReader(const TUcdFileReader& r);              //**not implemented**

then you'd get a linker error. Best fix would be (if possible) to implement them.

answered Feb 15 '14 at 06:40

TonyWilk

1,447
10
13

the only place that TUcdFileReader is called is : void ProcessComment(TUniChDb::TUcdFileReader &reader) I update this part in my question. Thanks for your hint, but I did not get how to fix this. – Omid Feb 15 '14 at 06:49
1

Assuming C++11, you can even mark your unwanted constructors `= delete` like this:`TUcdFileReader& operator = (const TUcdFileReader& r) = delete; ` to get a compilation error rather than a linker error (which you notice earlier). – Martin J. Feb 15 '14 at 07:03
@Martin J: didn't know that - really useful, ta. – TonyWilk Feb 15 '14 at 09:05

Segmentation fault driven of a null reference in a c++ header file

1 Answers1