unexpected SIGSEG ABORT when working with vector

Cheraphy (1730)
I keep getting a segmentation error when ever I have the following code...


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int main(void) {
    //Section 1
    unsigned long val = 12;
    std::vector<unsigned long> vval;
    for(unsigned long i = 0; i < 100; ++i) {
      vval.push_back((unsigned long)0);
    }
    //section 2
    bignum* bn1 = new bignum(val);
    delete bn1;
}



relevent constructor:

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bignum::bignum ( const unsigned long val ) {
    if(this->num == nullptr) {
        delete this->num
    }
    this->num = new std::vector<unsigned long> ( 1, val );
}


here's the thing, it only segfaults when both sections 1 and 2 are there. It runs fine when section 1 is alone, and when section 2 is alone.

bignum::num is defined as std::vector<unsigned long>*

Error: *** Error in `/home/alex/projects/bignum/build/bignum': free(): invalid pointer: 0x00007ffff75b5b88 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x80a46)[0x7ffff7274a46]


compiler is clang++ 3.2




edit:

It doesn't happen if I restructure it so that bignum::num is not a pointer to an std::vector<unsigned long>
Last edited on
norm b (337)
The following compiles fine here:
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#include <vector>

class bignum{
public:
    bignum(const unsigned long val);
private:
    std::vector<unsigned long> *num;
};

bignum::bignum ( const unsigned long val ) {
    if(this->num == nullptr) {
        delete this->num;
    }
    this->num = new std::vector<unsigned long> (1, val );
}

int main(void) {
    //Section 1
    unsigned long val = 12;
    std::vector<unsigned long> vval;
    for(unsigned long i = 0; i < 100; ++i) {
      vval.push_back((unsigned long)0);
    }
    //section 2
    bignum* bn1 = new bignum(val);
    delete bn1;
}

$ clang++ -v
Debian clang version 3.3-9 (branches/release_33) (based on LLVM 3.3)
Target: x86_64-pc-linux-gnu
Thread model: posix
Cheraphy (1730)
That looks identical to what I have, but still aborts. Potential bug?


edit: tried it with g++, should definitely not be a bug.

edit edit: ultimately gave up and left num a non pointer.
Last edited on
norm b (337)
tried it with g++, should definitely not be a bug.
no comprende. Did it work with g++?

If you c/p the code in my post does it compile?

EDIT: Whoops. Missed your edit edit.

Last edited on
naraku9333 (2163)
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bignum::bignum ( const unsigned long val ) {
    if(this->num == nullptr) {
        delete this->num
    }
    this->num = new std::vector<unsigned long> ( 1, val );
}

Shouldn't that be !=
norm b (337)
Good eye naraku9333. Missed that.
LB (13399)
But delete is just as happy with a null pointer as with a valid pointer - it just doesn't do anything if the pointer is null.
Cheraphy (1730)
Hurr. Durr. Simple errors, naraku, story of my life.


I've been programming in declarative languages for the last 2 years, trying to get back into C++ and a bloated bignum library is usually how I get into languages.
naraku9333 (2163)
L B wrote:
But delete is just as happy with a null pointer as with a valid pointer - it just doesn't do anything if the pointer is null.
True, and since it is in a ctor there's no chance of num being allocated already so the check isn't even necessary.
kulkarnisr (91)
You should add destructor in bignum to free num.

Cheraphy (1730)
It's there. Originally I just called it.
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