CODEWITHSUNDEEP
c++segmentation-fault
Aschab
Aschab

Reputation: 1399

How can I fix a segmentation fault on C++

Im trying to build this for the amd64arch and it keeps giving me segmentation fault:

    #include "client.h"

      namespace {

    class SimpleClientImpl : public SimpleClient {
    private:
      int progress_counter_;

    public:
      SimpleClientImpl() : progress_counter_(0) {}

      int GetProgress() const;
      char* CutPrefix(char* data);
    };

    int SimpleClientImpl::GetProgress() const {
      return progress_counter_;
    }

    char* SimpleClientImpl::CutPrefix(char* data) {
      progress_counter_++;
      return data + *reinterpret_cast<size_t*>(data) + sizeof(size_t);
    }

    }  // namespace

    std::shared_ptr<SimpleClient> CreateSimpleClient() {
      return std::shared_ptr<SimpleClient>(new SimpleClientImpl);
    }

In the client.h I got:

    #ifndef TEST_CLIENT_H_
    #define TEST_CLIENT_H_

    #include <memory>

    class SimpleClient {
    public:
      virtual int GetProgress() const = 0;
      virtual char* CutPrefix(char* data) = 0;
      virtual ~SimpleClient() {}
    };

    std::shared_ptr<SimpleClient> CreateSimpleClient();

    #endif

Any Idea of how can i fix this? I'm not sure why would it give me a segmentation fault, i've tryed runnin it as admin, but I dont really get where is the problem.

Upvotes: 0

Views: 164

Answers (2)

Mekap
Mekap

Reputation: 2085

 char* CutPrefix(char* data);

You may never allocate memory for that pointer on string (Either with new or the c malloc) ;

My guess is that you miswrote this line : 

return data + *reinterpret_cast<size_t*>(data) + sizeof(size_t);

And that you should either work with strings, or do your allocation correctly beforehands if you really want to keep working with char* in cpp.

Upvotes: 1

Peter
Peter

Reputation: 36617

Although you haven't shown calling code, it is presumably creating a SimpleClientImpl and passing (the address of) some character buffer to the CutPrefix() member function. Possibly repeatedly.

Check the data that is being supplied to CutPrefix(). Either it is not encoded in the form you assume (a length, followed by that number of characters) or the caller is walking past the end of the supplied buffer. Possibly both.

In either case, the caller will exhibit undefined behaviour if it uses the pointer returned.

Since you haven't provided the calling code, however, it is not possible to advise on how to fix the problem.

Upvotes: 0

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