Qt exit code 3

[Martinuccia_96]

I have a QtextEdit. To save all the characters that I insert on the edit block, I use a dynamic vector.
It is built in the following way:

std::vector<std::vector<symbol>> symbols

The starting dimension is 1 for the interior vector and 1 for the exterior vector.
symbol is a class:

symbol(wchar_t ch, int siteId, int counter, const std::vector<int> &pos, bool verified=false);

When I insert characters in a position that overcomes the dimension of the vector, I resize it, with the following method:

void document::checkIndex(unsigned int i0, unsigned int i1) {
    double mult_fac=1.5;
    if(i0>=symbols.capacity()){
        symbols.resize((i0+1)*mult_fac);

}
    if(i1>=symbols[i0].capacity())
        symbols[i0].resize((i1 + 1)*mult_fac, emptySymbol);

}

The problem is that sometimes, when I continue to insert characters on my QTextEditBlock as in the following picture:

my program crashed with the exit code3.
I think that it a problem of memory allocation, but I can't solve it.

[jsulm]

@Martinuccia_96 Not sure how your question is related to Qt.
Did you use debugger to find out where exactly it crashes?
Please do so and post the stacktrace after crash.