Running the Eclipse 3.4 formatter application

D:\gnu\eclipse\eclipse.exe -application org.eclipse.jdt.core.JavaCodeFormatter -config D:\gnu\jee\workspace\Concurrency\.settings\org.elipse.jdt.core.prefs d:\Foo.java

variable type checking in C

Put all the files in a directory. Run gcc *.c -o main.exe. The compilation will succeed. The reason is that C does not check type consistency of external variable declaration and reference.
1 one.c

int abc = 1;

2 main.c

#include <stdio.h>
extern float abc;
int main(void) {
    printf( "%f", abc );
}

Function type checking in C

Put all the following 3 files in a directory. Run gcc *.c. The compilation will succeed. And running the resulted excecutable file will print I am here, man!. Run g++ *.c The compilation will fail. The reason is that during linking, C only check function names. But C++ check function type.
1. caller.c

#include "callee.h"
int main(void) {
    foo();
}

2. callee.h

int foo(void);

3. callee.c

#include 
void foo(int v) {
    printf( "I am here, man!" );
}

Index overflow in Java for loop

The following little code snippet shows the overflow of for loop index in Java.

public class Out {
    public static void main(String[] ars) {
        for(int i = 0; i <= 2147483647 ; i+=100000000 )
        {
            System.out.println( i + "\n" );
        }        
    }
}

You may expect that the iteration count is 22. But it is not true. i is 2100000000 after the 22nd iteration. Then 100000000 is added to i(2100000000) again. 2200000000 is bigger than 2147483647. So int overflow will happen. i will become a negative integer. So the loop will continue.

For details of loop index overflow, you can refer to Programming Language Pragmatics.

Genenared methods values and valueOf for Enum

I have recently tried Java Enum when doing software development. The following code is an example:

public Enum FooType {
    ABC, DEF;
}

I found two methods valueOf and values in the Javadoc for my enum code. I did not write these 2 methods. And it's superclass java.lang.Enum<FooType> also does not have these 2 methods. Then I checked JLS 3.0. 8.9 Enums says these 2 methods are automatically generated. It is a little magic. One Java class can has methods which do not exist as source code. Too many magic which do not have a consistent rationale can make a language hard to learn and use.

Modula-2

I tried a little Modula-2 programming today. I used XDS 2.5. I built the following little program successfully in XDS IDE.

MODULE hello;
FROM InOut IMPORT WriteString, WriteLn;
BEGIN
    WriteString("Hello, world!");
    WriteLn;
END hello.

And I could use xc to compile it. The following error showed up when I used xlink to link it.

XDS Link  Version 2.6 Copyright (c) 1995-2001 Excelsior
Fatal error (13): No program entry point

I have googled answers for it and read XDS documentation. Unfornately, I can't find an answer. Again, it shows a quick start guide with some simple examples is extremely important for a beginner to use some new tools.

After wresting with xlink for some time , I worked out the following solution.

xlink hello.obj C:\free\XDS\LIB\x86\libxds.lib C:\free\XDS\LIB\x86\import32.lib C:\free\XDS\LIB\x86\xstart.lib

Reading of Programming Language Pragmatics

Programming Language Syntax

The following syntax shows dangling else problem of Pascal.

• stmt -> if condition then_clause else_clause | other_stmt


• then_clause -> then stmt


• else_clause -> else stmt | ε

Sometimes, we have a hard time to use some language. Sometimes it is not because we are not smart enough. It is because of the flaws of the programming language.