2007年3月22日
#
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?
:)
C++ operator precedence
http://www.cppreference.com/operator_precedence.html| Precedence | Operator | Description | Example | Associativity |
|---|
| 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 AND | flags = flags & 42; | left to right |
| 10 | ^ | Bitwise exclusive OR | flags = flags ^ 42; | left to right |
| 11 | | | Bitwise inclusive (normal) OR | flags = flags | 42; | left to right |
| 12 | && | Logical AND | if( conditionA && conditionB ) ... | left to right |
| 13 | || | Logical OR | if( 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 operator | for( i = 0, j = 0; i < 10; i++, j++ ) ... | left to right |
Finally, I find basic knowledge is important.
2006年3月24日
#
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.
2006年3月3日
#
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.
2006年3月1日
#
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:
.................
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.
2006年2月21日
#
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
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.
2006年2月20日
#
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.