J-XMoses

J-XMoses

2007年3月22日 #

typedef keyword in C++

read this article -> http://www.functionx.com/cpp/keywords/typedef.htm
It said that "The typedef keyword can be followed by an attribute before the data type. In its simplest form, the attribute can be that of an access level such as public, private, or protected." and provide a examples:


#include <iostream>
#include <string>
using namespace std;

typedef struct Student;
typedef class Country;

typedef public short SmallNumber;
typedef private unsigned int Positive;
typedef protected double* PDouble;
typedef public string FiveStrings[5];
typedef private double (*Addition)(double value1, double value2);

struct Student
{
	string FirstName;
	string LastName;
};

typedef struct _Empl
{
	string FullName;
	double HourlySalary;
}Employee;

class Country
{
	string Name;
	string Capital;
	string Code;
};

double Add(double x, double y)
{
	double result = x + y;
	return result;
}

typedef enum EmplStatus { esFullTime, esPartTime, esContractor };
typedef Student *PStudent;
typedef Country *PCountry;

int main()
{
	Student pupil;
	Country pais;
	EmplStatus emplst;
	PStudent ptrStd = new Student;
	PCountry pPais = new Country;

	return 0;
}


I found that I can't compile it on my Linux using g++.


[root@sd1 xxx]# g++ typedef.cpp -o typedef
typedef.cpp:8: error: expected unqualified-id before 'public'
typedef.cpp:9: error: expected unqualified-id before 'private'
typedef.cpp:10: error: expected unqualified-id before 'protected'
typedef.cpp:11: error: expected unqualified-id before 'public'
typedef.cpp:12: error: expected unqualified-id before 'private'


Why, can anybody tell me?
:)

posted @ 2007-03-22 17:48 Java-XMoses 阅读(392) | 评论 (0)编辑 收藏

C++ operator precedence

C++ operator precedence
http://www.cppreference.com/operator_precedence.html

PrecedenceOperatorDescriptionExampleAssociativity
1()
[]
->
.
::
++
--
Grouping operator
Array access
Member access from a pointer
Member access from an object
Scoping operator
Post-increment
Post-decrement
(a + b) / 4;
array[4] = 2;
ptr->age = 34;
obj.age = 34;
Class::age = 2;
for( i = 0; i < 10; i++ ) ...
for( i = 10; i > 0; i-- ) ...
left to right
2!
~
++
--
-
+
*
&
(type)
sizeof
Logical negation
Bitwise complement
Pre-increment
Pre-decrement
Unary minus
Unary plus
Dereference
Address of
Cast to a given type
Return size in bytes
if( !done ) ...
flags = ~flags;
for( i = 0; i < 10; ++i ) ...
for( i = 10; i > 0; --i ) ...
int i = -1;
int i = +1;
data = *ptr;
address = &obj;
int i = (int) floatNum;
int size = sizeof(floatNum);
right to left
3->*
.*
Member pointer selector
Member pointer selector
ptr->*var = 24;
obj.*var = 24;
left to right
4*
/
%
Multiplication
Division
Modulus
int i = 2 * 4;
float f = 10 / 3;
int rem = 4 % 3;
left to right
5+
-
Addition
Subtraction
int i = 2 + 3;
int i = 5 - 1;
left to right
6<<
>>
Bitwise shift left
Bitwise shift right
int flags = 33 << 1;
int flags = 33 >> 1;
left to right
7<
<=
>
>=
Comparison less-than
Comparison less-than-or-equal-to
Comparison greater-than
Comparison geater-than-or-equal-to
if( i < 42 ) ...
if( i <= 42 ) ...
if( i > 42 ) ...
if( i >= 42 ) ...
left to right
8==
!=
Comparison equal-to
Comparison not-equal-to
if( i == 42 ) ...
if( i != 42 ) ...
left to right
9&Bitwise ANDflags = flags & 42;left to right
10^Bitwise exclusive ORflags = flags ^ 42;left to right
11|Bitwise inclusive (normal) ORflags = flags | 42;left to right
12&&Logical ANDif( conditionA && conditionB ) ...left to right
13||Logical ORif( conditionA || conditionB ) ...left to right
14? :Ternary conditional (if-then-else)int i = (a > b) ? a : b;right to left
15=
+=
-=
*=
/=
%=
&=
^=
|=
<<=
>>=
Assignment operator
Increment and assign
Decrement and assign
Multiply and assign
Divide and assign
Modulo and assign
Bitwise AND and assign
Bitwise exclusive OR and assign
Bitwise inclusive (normal) OR and assign
Bitwise shift left and assign
Bitwise shift right and assign
int a = b;
a += 3;
b -= 4;
a *= 5;
a /= 2;
a %= 3;
flags &= new_flags;
flags ^= new_flags;
flags |= new_flags;
flags <<= 2;
flags >>= 2;
right to left
16,Sequential evaluation operatorfor( i = 0, j = 0; i < 10; i++, j++ ) ...left to right


Finally, I find basic knowledge is important.

posted @ 2007-03-22 17:11 Java-XMoses 阅读(193) | 评论 (0)编辑 收藏

2006年3月24日 #

I know Why I failed so many times in trying to connect mysql installed on other server

Once upon a time, I see on some document telling that "updating the host field of user record to % can enable user connect to the mysql database from any host", so I followed the guide,tried from other side and failed.
Today I finally found the reason:
You need exec reload to make the change take effect using "./mysqladmim -uroot -p<your password> reload"

So I can connect from other PC to the mysql Server.

Just trick, but very useful.

posted @ 2006-03-24 21:42 Java-XMoses 阅读(216) | 评论 (0)编辑 收藏

2006年3月3日 #

kbps or Kbps

Short for kilobits per second, a measure of data transfer speed. Modems, for example, are measured in Kbps. Note that one Kbps is 1,000 bits per second, whereas a KB (kilobyte) is 1,024 bytes. Data transfer rates are measured using the decimal meaning of K whereas data storage is measured using the powers-of-2 meaning of K. Technically, kbps should be spelled with a lowercase k to indicate that it is decimal but almost everyone spells it with a capital K.

posted @ 2006-03-03 17:40 Java-XMoses 阅读(126) | 评论 (0)编辑 收藏

2006年3月1日 #

The META-INF directory in the JAR file

The META-INF directory, if it exists, is used to store package and extension configuration data, including security, versioning, extension and services.
The following files/directories in the META-INF directory are recognized and interpreted by the Java 2 Platform to configure applications, extensions, class loaders
and services:

  • MANIFEST.MF

.................

Tag libraries should be packed with their .tlds packed in their META-INF directory. JSP engines look through the JAR files in the /lib directory for TLDs and add the tags as necessary. Then when you are installing tag libraries, you only need to deliver one file - the JAR - no changes to the web.xml, no extra tlds hanging around.

posted @ 2006-03-01 21:39 Java-XMoses 阅读(287) | 评论 (0)编辑 收藏

2006年2月21日 #

Use the DBCP in Application that running multiple threads

Just use the BasicDataSourceFactory,
I will write a snippet of code to test the DBCP. How should I do ?? Hmmm~~~
Let me try and give out a test result.

I am a tester

posted @ 2006-02-21 16:34 Java-XMoses 阅读(128) | 评论 (0)编辑 收藏

Route selection in routing table

Multiple routes with same prefix(IP address and Netmask) can exist in the routing table.Where the routing table contains multiple routes to the same destination,the preference values of each router are compared. The route that has the lowest preference value is selected. If the preference values are the same, the metrics values are then compared.The route that has the lowest metric value is then selected.

posted @ 2006-02-21 09:58 Java-XMoses 阅读(194) | 评论 (0)编辑 收藏

2006年2月20日 #

Why the select method of JTextArea don't take effect.

In my swing UI, there is JTextArea component named "textarea_webpage", I want to mark some sentence in the textarea as marked using program just as user selecting them using mouse.
------------------------------------------------------------Code Below-------------------------------------------------
textarea_webpage.setSelectionColor(Color.black);
textarea_webpage.setSelectedTextColor(Color.white);
textarea_webpage.setSelectedTextColor(Color.white);
textarea_webpage.select(urlItem.getStart(),urlItem.getEnd()); // the urlItem is self-defined object to store positon information of certain sentences
----------------------------------------------------------------------------------------------------------------------------

Every time the code is executed, there is nothing take place in my textarea.
After goolge for the answer in the net.
I found that I forgot the code 
         
textarea_webpage.getCaret().setSelectionVisible(true);

There are so many tricks in Swing designing, I'm just a beginner.
Pay more attention.

posted @ 2006-02-20 13:32 Java-XMoses 阅读(288) | 评论 (1)编辑 收藏

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