where the segmentation fault is generated in this code? [closed]

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 11 years ago.

class Transaction  //TO store a transaction read from file
{
public:
    int maxlenth;
    int length1,length2;
    vector<string> *items;
    vector<int>  *share; 
    int tmv;

    Transaction():maxlenth(Translen),length1(0),length2(0)
    {
        items=new vector<string>(maxlenth);
        share=new vector<int>(maxlenth);
    }
    ~Transaction()    
    {
        delete items;
        delete share;
    }

    void set_tmv()
    {
        tmv=0;
        for(int i=0;i<=length2;i++)
               tmv=tmv+(*share)[i];
    }     
};


class Data
{
public:
    ifstream in;

    Data(char *filename);
    ~Data();

    Transaction& getnextTransaction(Transaction &Trans);
};


Data::Data(char *filename)
{
    ifstream in(filename);
        assure(in,filename);
}

Data::~Data()
{
    in.close(); 
}

Transaction&  Data::getnextTransaction(Transaction &Trans)
{
    const char* delimiters =
    开发者_高级运维      "  \t;()\"<>:{}[]+-=&*#.,/\\~";

    //ifstream in("testdata.txt");
    //set<string>Items1;
    vector<string> v(5);
    int i=0;
    string line;
    getline(in, line); 

    char* s =strtok((char*)line.c_str(), delimiters);
    while(s) 
    {
        if(i==v.size())
            v.resize(v.size()*2);

        v[i++]=s;
        s = strtok(0, delimiters);
    }
    vector<string>::iterator it=v.begin();
    int j=0;
    while(j<50)
    {
        (*Trans.items)[(Trans.length1)++]=v[j];
        j=j+2;
    }
    j=1;
    while(j<=50)
    {
        (*Trans.share)[Trans.length2++]=(atoi(v[j].c_str()));
        j=j+2;
    }

    //copy(v.begin(),v.end(),ostream_iterator<string>(cout,"\n");
    return Trans;
}

int main()
{
    Data d("testdata.txt");
    Transaction t,q;

    d.getnextTransaction(t);
    t.set_tmv();

    return 0;
}

While I am debugging with gdb, I am geting something like:

Programm recieved SIGSEGV segmentation fault in std::string::assign(std::string const &)

While I am including the line ifstream in("testdata.txt") in function getNexttransaction(), I am not getting any error.

What's going wrong?

---

well, i did not read your code so i dont know what its purpose is, but if its an usual c++ application and nothing to modify the systems default memory management, you should learn using GDB.

http://www.unknownroad.com/rtfm/gdbtut/gdbsegfault.html

helps a lot removing those nasty segfaults, it will just take you 5 minutes to read it and use it, but can save you hours of printf debugging. (sorry but reading through that much code to find a wrong reference to some memory would be hard-work)

---

How can you be absolutely sure that your vector v will have 50 elements in it, and no amount that is less? In this while-loop,

while(j<50)
{
  (*Trans.items)[(Trans.length1)++]=v[j];
  j=j+2;
}

you're accessing up to 50 members for the vector v since you're making calls to v[j], and j will go up to 49, but if v.size() != 50, then you're going to get a segmentation fault. Since you initialize v to be only 5 elements, and only resize it if you increment past it's current max-size, that means will have at least 5 or more members in v, but that does not mean there will be at least 50 members. The same is true for the second while-loop using the value of j as well.

---

After hacking the code a bit so that it would compile. I get this from valgrind:

bash> valgrind ./a.out

Invalid read of size 4
==1827==    at 0xDE038: std::string::assign(std::string const&) (in /usr/lib/libstdc++.6.0.4.dylib)
==1827==    by 0x282B: Data::getnextTransaction(Transaction&) (dummy.cpp:88)
==1827==    by 0x2947: main (dummy.cpp:110)
==1827==  Address 0x3ec6d8 is 4 bytes after a block of size 20 alloc'd
==1827==    at 0x1A6BB: operator new(unsigned long) (vg_replace_malloc.c:261)

Line 88 is right inside your main read loop. Suggesting that your loop may be confused.

This may not be your problem. (As I had to comment out assure to get it to compile, and I dont have your data file...) But you could use a similar method to get the real culprit.

---

EDIT: (Removed section about dereferencing Trans)

Translen might be your problem in this particular case. If it's less than 50, you're going to exceed the length of the items and share arrays during the while(j<50) loop in getnextTransaction. Jason's answer elaborates on this point.