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  Shell script common interview questions

Shell script is frequently used when monitoring system status on Linux. It's not an easy task to write shell script but it's a very important skill for developers and system administrators to ease work and automate common tasks. This post will share some common interview questions about shell script. 1. Get random characters(8 characters) Method 1 # echo $RANDOM |md5sum |cut -c 1-8 471b94f2 Method 2 # openssl rand -base64 4 vg3BEg== Method 3 # cat /proc/sys/kernel/random/uuid |cut -c 1-8 ed...

   LINUX,INTERVIEW,SHELL SCRIPT     2018-09-28 10:46:00

  Understanding PHP's internal function definitions

Welcome to the second part of the “PHP’s Source Code For PHP Developers” series. In the previous part ircmaxell explained where you can find the PHP source code and how it is basically structured and also gave a small introduction to C (as that’s the language PHP is written in). If you missed that post, you probably should read it before starting with this one. What we’ll cover in this article is locating the definitions of internal functions in t...

   PHP,internal function,definition,rationale     2012-03-16 10:46:26

  Use DTrace to diagnose gdb issues

A few days ago, I installed the newest 64-bit gdb program (version 7.7.1) on Solaris 10 (X86_64 platform) to debug programs. After playing with the gdb a day, I found 2 issues about gdb:(1) The "set follow-fork-mode child" command doesn't take effect. By default, after the parent process forks the child process, the gdb will track the parent process, so this command can make gdb begin to follow the child process. But this command works OK on Linux.(2) The gdb can't parse the 32-bit application c...

   DTrace, debug, gdb, UNIX     2014-06-28 05:11:20

  A Tiny MySQL++ Tutorial; C++ and MySQL; MySQL++ Example

I wrote a post about how to install MySQL++ and I thought I will write a quick tutorial on how to use it too. This is a very basic MySQL++ program and it’s very self explanatory: #include <mysql++.h> #include <stdlib.h>   using namespace std; using namespace mysqlpp;   int main() { try { Connection conn(false); conn.connect("DB NAME", "DB HOST probably localhost", "DB USER", "DB PASS"); Query query = conn.query(); } catch (BadQuery er...

   C++,Example,MySQL++,Insert,API     2011-09-05 02:12:40

  Pointers, arrays, and string literals

A recently posted question on Stack Overflow highlighted a common misconception about the role of pointers and arrays held by many programmers learning C.The confusion stems from a misunderstanding concerning the role of pointers and strings in C. A pointer is an address in memory. It often points to an index in an array, such as in the function strtoupper in the following code:void strtoupper(char *str) { if (str) { // null ptr check, courtesy of Michael while (...

   char pointer,initialization,literal,cann     2011-09-22 13:29:23

  When and How to Use the Go Channel

Go’s concise structure and powerful native library enable us to hit the ground running easily. It is more efficient than Java or Python when implementing the same functions, especially its concurrent programming, which is very handy and widely admired due to its goroutine and channel. goroutine and channel has much to dig into, and let’s start with channel, which I used to consider narrowly as a message queue to transfer data between gorouti...

   GOLANG,CONTEXT,CHANNEL     2022-09-17 23:06:36

  Integer overflow

You may be familiar with integer overflow, but what you may not be familiar with is how gcc handles signed integer overflow. First let's look at the standard, for unsigned integer, the standard says : A computation involving unsigned operands can never overflow, because a result that cannot be represented by the resulting unsigned integer type is reduced modulo the number that is one greater than the largest value that can be represented by the resulting type. In other words, unsigned integer ov...

   Integer overflow,gcc,Linux     2012-10-20 13:33:10

  C++11 multithreading tutorial

The code for this tutorial is on GitHub: https://github.com/sol-prog/threads. In my previous tutorials I’ve presented some of the newest C++11 additions to the language: regular expressions, raw strings and lambdas. Perhaps one of the biggest change to the language is the addition of multithreading support. Before C++11, it was possible to target multicore computers using OS facilities (pthreads on Unix like systems) or libraries like OpenMP and MPI. This tutorial is meant to get you st...

   C++,Multithreading,Standard 11,Demo     2011-12-18 00:50:35

  Select top 3 values from each group in a table with SQL

Yesterday, my friend Liu Bing asked me a question about how to select top 3 values for each person in a database table using SQL. I think this question is interesting and it deserves some thoughts. Here I record down how to solve this issue. Assume we have a table which has two columns, one column contains the names of some people and the other column contains some values related to each person. One person can have more than one value. Each value has a numeric type. The question is we want to se...

   SQL,Correlated query,top 3     2013-05-23 03:21:25

  What is the use of empty struct in GoLang

In Go, an empty struct struct{} is a struct with no fields that may appear to be of little use, but in reality, it can be useful in certain situations and become a simple and efficient solution in code. As a semaphore or lock Because the empty struct has no fields, it can be conveniently used to implement some concurrency control functions, such as mutex locks, read-write locks. We can use chan struct{} to implement an unbuffered channel for controlling concurrent access. package main import ( ...

   GOLANG,EMPTY STRUCT     2024-04-05 23:54:03

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