glibc detected free() invalid size (fast) error?

Question

I'm getting this error when I execute the following function and I have no idea what it means. Here is the function:

void readf2()
{
    std::ifstream inFile("f2",std::ios_base::binary);
    std::string str(2, '\0');
    int i = 0;
    while(inFile.read(&str[i],2)){
    cout<<"Success: ["<< i << "] = "<< (int)str[i];                        ;
    cout<<"\n";
    i++;
    }
}

The function works for a while writing various numbers to the console and then boom it crashes with this error, a backtrace, and a memory map. Is this happening because I am freeing a memory address that doesn't exist?

Answer 1

Most likely you're giving the read call a pointer to memory that doesn't belong to you.

str[i] returns an offset in the string, but it doesn't guarantee that you have enough memory to read to that location (+2).

What you probably meant was to have an array of int s, and use the i as an index on that:

void readf2()
{
    std::ifstream inFile("f2",std::ios_base::binary);
    std::vector< int >  str; // if you're reading int's - use int, not string
    int i = 0;
    int j;
    while(inFile.read(&j,sizeof(int))){ // check what the content is here
    str.push_back(j);
    cout<<"Success: ["<< i << "] = "<< str[i];
    cout<<"\n";
    i++;
    }
}