C++ - Any way to emulate an "eval"?

Question

You have a string in C++ representing an expression, e.g. "3%2+4*3". Any way in C++ to evaluate the expression, in the example to 13?

Answer 1

There is no eval equivalent in C/C++. You will have to write rules to parse the string yourself, or you can create a program which compiles and invokes specific code segments - An easier hack but most likely platform dependent.

int main() {
std::string expr = "1+1";
std::ofstream obj;
// output expr to .cpp file
// call gcc/c++ to compile .cpp
// run the output file
}

Answer 2

Hatsy Rei i just tried to use that code to test it and it doesnt work

Answer 3

Dangerzone47

"It doesn't work" is a really vague statement especially when the "code" I gave is merely a very general concept of how it should work. If you need help, post your code.

Answer 4

Sorry Hatsy Rei i forgot to say the error. It says: error: aggregate 'std::ofstream obj' had incomplete type and cannot be defined. the code is really a copy/paste of yours with an output statement with it, to test.

Answer 5

Dangerzone47 You still did not show your code, but I'll just assume you didn't include the header for file streams.

http://www.cplusplus.com/reference/fstream/fstream/

https://stackoverflow.com/questions/1057287/ofstream-error-in-c

Answer 6

Yep wrong lib. Thx Hatsy Rei

Answer 7

I dont know anything about C++ but is there a way to type cast maybe?

Edit: http://www.cplusplus.com/doc/oldtutorial/typecasting/