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How can I validate a string to only allow alphanumeric characters in it?
...n I validate a string using Regular Expressions to only allow alphanumeric characters in it?
10 Answers
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Single quotes vs. double quotes in C or C++
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In C and in C++ single quotes identify a single character, while double quotes create a string literal. 'a' is a single a character literal, while "a" is a string literal containing an 'a' and a null terminator (that is a 2 char array).
In C++ the type of a character lite...
Which MySQL datatype to use for an IP address? [duplicate]
...nvert them:
INSERT INTO `table` (`ipv4`) VALUES (INET_ATON("127.0.0.1"));
SELECT INET_NTOA(`ipv4`) FROM `table`;
For IPv6 addresses you could use a BINARY instead:
`ipv6` BINARY(16)
And use PHP’s inet_pton and inet_ntop for conversion:
'INSERT INTO `table` (`ipv6`) VALUES ("'.mysqli_real_es...
Base64 length calculation?
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Each character is used to represent 6 bits (log2(64) = 6).
Therefore 4 chars are used to represent 4 * 6 = 24 bits = 3 bytes.
So you need 4*(n/3) chars to represent n bytes, and this needs to be rounded up to a multiple of 4.
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What does int argc, char *argv[] mean?
...ention, but they can be given any valid identifier: int main(int num_args, char** arg_strings) is equally valid.
They can also be omitted entirely, yielding int main(), if you do not intend to process command line arguments.
Try the following program:
#include <iostream>
int main(int argc,...
Difference between BYTE and CHAR in column datatypes
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Let us assume the database character set is UTF-8, which is the recommended setting in recent versions of Oracle. In this case, some characters take more than 1 byte to store in the database.
If you define the field as VARCHAR2(11 BYTE), Oracle can us...
What is the difference between static_cast and C style casting?
...situations where all that is needed is a simple conversion. The ability to select between several different casting operators of differing degrees of power can prevent programmers from inadvertently casting to an incorrect type.
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NULL values inside NOT IN clause
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Query A is the same as:
select 'true' where 3 = 1 or 3 = 2 or 3 = 3 or 3 = null
Since 3 = 3 is true, you get a result.
Query B is the same as:
select 'true' where 3 <> 1 and 3 <> 2 and 3 <> null
When ansi_nulls is on, 3 <&...
What belongs in an educational tool to demonstrate the unwarranted assumptions people make in C/C++?
...lo"); /* printf() returns the number of
characters successfully printed by it
*/
}
int World()
{
return printf("World !");
}
int main()
{
int a = Hello() + World(); //might print Hello World! or World! Hell...
[精华] VC中BSTR、Char和CString类型的转换 - C/C++ - 清泛网 - 专注C/C++及内核技术
[精华] VC中BSTR、Char和CString类型的转换char*转换成CString，CString转换成char*，BSTR转换成char*，char*转换成BSTR，CString转换成BSTR，BSTR转换成CString，ANSI、Unicode和宽字符之间的转换...1、char*转换成CString
若将char*转换成CString，除了直接...