I have been working on a basic calculator that can take in complicated mathematical expressions such as:(2-4)*7/(3/4) etc etc
I am using an implementation of the shunting yard algorithm...
I am on a linux OS. using the gdb debugger I have isolated a segmentation fault to one function. using cout statements I have isolated it further to a single line..however I cannot fathom why this line is giving me a segfault..I will give more info on exactly where in just a moment, first here is some code..
bool infixToPostfix(const std::vector<std::string>& inputTokens, const int& size, std::vector<std::string>& strArray){
std::cout << "1" << std::endl;
bool success = true;
std::list<std::string> out;
std::stack<std::string> st;
for(int i = 0; i < size; i++){
std::cout << "2\n";
const std::string token = inputTokens[i];
if(isOperator(token)){
std::cout << "3\n";
const std::string o1 = token;
if(!st.empty()){
std::cout << "4\n";
std::string o2 = st.top();
while(isOperator(o2) && ((isAssociative(o1, LEFT_ASSOC) && cmpPrecedence(o1, o2) == 0) || (cmpPrecedence(o1, o2) < 0))){
std::cout << "5\n";
st.pop();
out.push_back(o2);
if(!st.empty()){
std::cout << " 6\n";
o2 = st.top();
}
else{
std::cout << "7\n";
break;
}
}
}
std::cout << "8\n";
st.push(o1);
}
else if(token == "("){
std::cout << "9\n";
st.push(token);
}
else if(token == ")"){
std::cout << "10\n";
std::string topToken = st.top();
while(topToken != "("){
std::cout << "11\n";
out.push_back(topToken);
st.pop();
if(st.empty() ){
std::cout<< "12\n";
break;
}
std::cout << "13\n";
topToken = st.top();
}
if(!st.empty()){
std::cout << "14\n";
st.pop();
}
if(topToken != "("){
std::cout << "15\n";
return false;
}
}
else{
std:: cout << "16\n";
out.push_back(token);
}
}
while(!st.empty()){
std:: cout << "17\n";
const std::string stackToken = st.top();
if(isParentheses(stackToken)){
std::cout << "18\n";
return false;
}
std::cout << "19\n";
out.push_back(stackToken);
st.pop();
}
std::cout << "20\n";
strArray.assign(out.begin(), out.end());
return success;
}
the segfault is occurring at std::cout << "10\n"; when calling std::string topToken = st.top();
I will give some input/outputs
intput: (8*2)
outputs: 1
2
9
2
3
4
8
2
3
4
5
6
8
2
10
11
13
14
2
10
segfault (core dumped)
input: (4/4)
output: 1
2
9
2
3
4
8
2
3
4
5
6
8
2
10
11
13
14
2
10
segfault (core dump)
there are a few more tests I ran that I could easily post here but they become very redundant, honestly. If you guys want to see more you need just ask and I will gladly provide more. However I feel like these two should provide enough info...
I know where the segfault is occurring and I have a hunch as to why..so if anyone can confirm to me why exactly the fault is happening that'd be great, and any solutions to the problem would be much appreciated.
P.S: any typos in the code are typos! I copied the code by retyping it since I am coding on a linux OS but I own a pc. With that being said...the code compiles without errors, any misspelled terms are typos!!
thanks again
EDIT: after giving it a few days and coming back to this I ran a few more tests on the code. This time using equations without parentheses.
input:3-9
output:1
2
3
8
2
3
4
5
7
8
17
19
20
segfault (core dump)
input:6/8
output:
1
2
3
8
2
3
4
5
7
8
17
19
20
So I am also getting a segfault when calling strArray.assign( out.begin(), out.end() );
Add the following after the line const std::string token = inputTokens[i];:
std::cout << "inputTokens[" << i << "]: " << token << std::endl;
I think you'll find that there's a problem with the inputTokens vector or possibly size isn't correct.
Out of curiosity - why do you pass in size as an argument instead of using inputTokens.size()?