Programming Tutorials

Programming errors a compiler will detect in C++

By: Stanley B. in C++ Tutorials on 2011-02-19  

Part of the compiler's job is to look for errors in the program text. A compiler cannot detect whether the meaning of a program is correct, but it can detect errors in the form of the program. The following are the most common kinds of errors a compiler will detect.

Syntax errors. The programmer has made a grammatical error in the C++ language. The following program illustrates common syntax errors; each comment describes the error on the following line:

// error: missing ')' in parameter list for main
int main ( {
// error: used colon, not a semicolon after endl
std::cout << "Read each file." << std::endl:
// error: missing quotes around string literal
std::cout << Update master. << std::endl;
// ok: no errors on this line
std::cout << "Write new master." <<std::endl;
// error: missing ';' on return statement
return 0
}

Type errors. Each item of data in C++ has an associated type. The value 10, for example, is an integer. The word "hello" surrounded by double quotation marks is a string literal. One example of a type error is passing a string literal to a function that expects an integer argument.

Declaration errors. Every name used in a C++ program must be declared before it is used. Failure to declare a name usually results in an error message. The two most common declaration errors are to forget to use std:: when accessing a name from the library or to inadvertently misspell the name of an identifier:

#include <iostream>
int main()
{
int v1, v2;
std::cin >> v >> v2; // error: uses " v "not" v1"
// cout not defined, should be std::cout
cout << v1 + v2 << std::endl;
return 0;
}

An error message contains a line number and a brief description of what the compiler believes we have done wrong. It is a good practice to correct errors in the sequence they are reported. Often a single error can have a cascading effect and cause a compiler to report more errors than actually are present. It is also a good idea to recompile the code after each fixor after making at most a small number of obvious fixes. This cycle is known as edit-compile-debug.