non-standard syntax use '&' to create a pointer to member c++ - c++

Question

I have created two vectors o3 ( a vector to hold the words from a string) and o4 ( a vector to hold those vector of words). In the if statement, once ";" has been found in the vectoro3[i], I want to stop putting words from thato3[i]` into o4, and go to the next line held in o3. I am getting the error "non-standard syntax use '&' to create a pointer to member c++" in the line commented as ERROR. Any help is highly appreciated. Thanks!
while (getline(myfile, line, (char)32)) // first read entire line into a
//string
// problem : this also reads empty lines
// and gives error
// while returning words
{
abc2.push_back(line); // inserting individual strings into a vector
//cout << abc[i] << "\n"; // use this to see
// them as a vector of lines
//i++;
}
for (int i = 0; i < abc.size(); i++)
{
single_line = abc[i];
if (((single_line[0] >= 'A') && (single_line[0] <= 'Z')) ||
((single_line[0] >= 'a') && (single_line[0] <= 'z')))
{
if (abc[i] != "")
{
o3 = output_words(abc[i], (char)32); // function to separate
//words in a line
int j1 = 0; int j2 = 0;
while (j2 < o3.size())
{
if (o3[j2] != "" && "\t") // *IMP* require this line to
// get words
// irrespective of spaces
{
if (o3[j2].find != ";") // ERROR
{
o4.resize(i + 1);// NO CLUE WHY IT WORKED WITH
// i+1 resize???!!!
o4[i].push_back(o3[j2]);
j2++;
}
else
{
j2++;
}
}
else
{
j2++;
}
}
}
}
else
{
o3 = { "" }; // o1 will be null vector (i.e will contain
// nothing inside)
o4.push_back(o3);
}
}

Answer 1

The result of expression o3[j2].find is a member of o3[j2] by the name find. That result is then compared with the string literal in the full expression o3[j2].find != ";".
The warning message seems to imply, that decltype(o3[j2])::find is a member function. In this context, the name of the member function decays to a member function pointer. The compiler warns you because such implicit conversion is ill-formed according to the standard, but supported as a language extension by the compiler. The standard way is to use the address-of operator & explicitly.
Comparing (a pointer to) a member function to a string literal makes little sense. You may have intended to call the member function instead. To call a function, you add the argument list surrounded by parenthesis: o3[j2].find(/* arguments */).
Assuming decltype(o3[j2]) is std::string (you forgot to declare o3), then the comparison with string literal also seems suspicious. std::string::find returns the index of the found substring or character. Comparing an integer to a string literal doesn't make any sense either. I recommend pondering what that line is supposed to do.