Syntax error

Syntax errors are generally violations of the syntax rules of a language. In computer science, the word usually refers to the so-called context- free portion of the syntactic rules of a programming language. Programs with syntax errors will be rejected by a compiler or interpreter. That does not change the fact that a syntactically correct program content may be wrong because it contains semantic errors.

Definition

Syntax errors are detected by the parser in the analysis phase of a compiler run, more precisely in the syntactic analysis. Here, the parser must not only recognize that the analyzed source code does not match the formal grammar of the programming language, but also output a meaningful error message. Since this does not describe all the features of a programming language by context-free grammars, are some errors detected violations of the rules of the programming type, even in the semantic analysis by the compiler, for example. Other flaw in the program can not detect at compile time; Compiler add there, however, often a code, which leads to a runtime error only during program execution. In contrast, let semantic errors, ie errors in the intended meaning of a program text, not at all recognize by machine.

Example

In many cases, syntax errors are caused by misplaced or missing characters such as semicolons, commas, and parentheses or meaningful words like for or BEGIN. Integrated development environments are generally constructed so that such errors are detected immediately and are signaled to the programmer.

An example of a syntax error in Java:

Public class Example {      public static void main ( String [ ] args ) {          System.out.println ("Hello World !")      } } A typical Java compiler would complain about the missing semicolon in this example in row 3 behind the closing bracket, as required by the Java syntax. The output of the compiler gives the programmer notes on type and approximate location of the error:

Syntax error, insert ";" to complete block statements Example.java line 3 This is usually the file name of the source text, the line and the actual error message is issued. The order and number of outputs varies from compiler to compiler.