Calculator.cpp example issue : Non-void function does not return a value in all control paths

[chrinkus]

Calculator.cpp example issue : Non-void function does not return a value in all control paths

[Chrinkus]

Thanks for pointing this out! When I did these exercises I was not very knowledgeable about compiler flags and the more rigorous error checking that could be employed. I assume that when XCode compiles C programs it adds some flags that warn about this behaviour and/or treat warnings as errors and refuse to compile.

That particular function has a switch with a default case. The default case has an elaborate if chain too. Every path through has a return statement so there is no way of reaching the end of the function. If control DOES reach the end there is the error() call. This is a function that is in the std_lib_facilities.h header that bootstraps us through the first part of the text. It's got a lot going on in it but the error function can be found at line 137. It takes a string and throws the error, effectively unwinding the stack and exiting the function through a giant gaping hole in the wall.

In your own code you can add a return Token{0}; at the end of the get function and that should convince XCode.

Let me know here if it works.

[acratophorux]

Yes, using return Token{0}; does solve the problem for the time being and shuts off the Xcode error/warning; though I am not sure that returning Token{0} won’t interfere with and cause further problems when the output of get() is used in the program. But, again, as you said, there is no way of reaching the end of the function, so I guess it is sufficient for now.

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Just to bring it to your notice, the same problem also lies in the Symbol_table::get_value(string s) function.

double Symbol_table::get_value(string s)    // return the value of the Variable names s
{
    for(const Variable& v : var_table)
        if(v.name == s) return v.value;
    error("get : undefined variable", s);
    //return 0;
} 

Here, returning any value other than v.value is a logical error which leaves us with no workaround.

To me, the problem seems to be attached with error() function as it does not return the type of the value to be supposedly returned by the function in which error() function is used.

[Chrinkus]

It's the same thing. If we get that far in the function we have an error. Rather than return an error value like in C we throw an error and rely on the caller to catch it. It's unfortunate that XCode doesn't detect the throw.