Sample Modern C++ Programs

Reverse Polish Notation Interpreter for math computation

Program

Source code:

src/sample-programs/rpn-calculator.cpp

Gist: Better for online visualization.

rpn-calculator.cpp

Online Compiler:

https://repl.it/repls/WiltedHoneydewClients

This code is a reverse polish notation (RPN) interactive interpreter for math computation based on a subset of the old Forth programming language.

The RPN notation may look award, but it is very practical and convenient for manual calculations and implementation of parsers, evaluators and interpreters. As a result, those RPN features have inspired some programming languages like:

Forth programming language
PostScript
Factor programming language
RPL - HP Calculators - programming language
dc (computer program) - Wikipedia
HP ( Hewlett-Packard ) Calculators RPN Calculators such as:
- HP 48 series - family of scientific and engineering calculators which uses RPN notation.
- HP-12C - Financial calculator with RPN notation.

Notes:

This math evaluator can be extended for implementing some embedded scripting language.
Modern C++ Features used:
- Dynamic Polymorphism, aka subtyping polymorphism.
- Template metaprogramming for the generic stack container.
- Smart Pointers for resource management.
- C++11 Lambdas and std::function
- C++ exceptions for error handling.

Compile:

$ clang++ rpn-calculator.cpp -o rpn-calculator.bin  -Wall -Wextra -std=c++1z -g

Running:

$ ./rpn-calculator.bin 
 EXPR+> 10 20 +
 stack:  30
 EXPR+> 50 - 
 stack:  -20

 EXPR+> 10 *
 stack:  -200
 EXPR+> 300 +
 stack:  100

 stack:  100

 EXPR+> M_PI 2 / sin
 stack:  100 1

 EXPR+> M_PI 2 / cos
 stack:  100 1 6.12323e-17

 EXPR+> M_LN10 exp
 stack:  100 1 6.12323e-17 10

 EXPR+> clear
 stack: 

 EXPR+> 30 dup
 stack:  30 30

 EXPR+> 40 dup
 stack:  30 30 40 40

 EXPR+> clear
 stack: 

 EXPR+> 30 dup *
 stack:  900

 EXPR+> 40 dup *
 stack:  900 1600
 EXPR+> +
 stack:  2500

 EXPR+> sqrt
 stack:  50

 EXPR+> 30 dup * 40 dup * + sqrt
 stack:  50 50
 EXPR+> 

 EXPR+> quit
 Exiting REPL OK.

Linux/Posix Daemon with syslog

This sample program is an Posix daemon encapsulated in a class which runs in background, even when the terminal is closed and logs to syslog a hypothetical commodity price simulated by a random number.

The program was tested on Linux, however it may work in any other compatible Posix operating system such as BSD, MacOSX and so on.

Code:

src/sample-programs/posix-daemon.cpp

Modern C++ Features used:

std::functions is used for callback and inject behavior in the PosixDaemon class.
C++11 auto syntax for functions and variables.
Deleted copy constructor and copy-assignment operator.
C++11 random number facilities.

Posix and Linux APIs used:

syslog
close() system calls
fork()
umaks()

See:

Daemon (computing) - Wikipedia
Fork (system call) - Wikipedia
Fork–exec - Wikipedia

Parts

Class PosixDaemon:

Encapsulates the U-nix and Posix daemon.

class PosixDaemon{
public:
     using Action = std::function<bool ()>;

     PosixDaemon(std::string path, std::string pidfile,  Action action)
      : m_path(std::move(path)),
        m_pidfile(std::move(pidfile)),
        m_action(action) { }
     ~PosixDaemon(){}	

     // Disable copy constructor in order to forbid copy 
     PosixDaemon(const PosixDaemon&) = delete;
     // Disable copy-assignment operator to make the class non-copiable.
     PosixDaemon& operator= (const PosixDaemon&) = delete;

     auto run() -> void {
         // Make child process
         pid_t child_pid = fork();
         if(child_pid < 0){
             std::cerr << "Error: failed to fork this process." << "\n";
             return;
         }
         if(child_pid > 0){
            std::cout << "Process ID of child process = " << child_pid << "\n";
            return;
         }
         // Umask file mode
         ::umask(0);
         // Set new session
         pid_t sid = ::setsid();
         if(sid < 0)
                 return;
         //------ Code of Forked Process ---------//
         // Set path of forked process (daemon)
         ::chdir(m_path.c_str());

         // Check whether there is a running process of this program 
         auto fs = std::ifstream(m_pidfile);
         if(fs.good()){
            int pid;
            fs >> pid;
            std::cerr << " [LOG] Kill process of PID = " << pid << "\n";
            ::kill(-pid, SIGTERM);
            fs.close();							
         }
         auto fo = std::ofstream(m_pidfile);
         if(fo.good()){
             int pid = ::getpid();
             std::cerr << "Child PID = " << pid << "\n";
             fo << pid  << std::flush;
         } else {
             std::cerr << " [LOG] Error: could not open PID file " << m_pidfile << "\n";
             return;
         }	
         // Close stdin, stdout and stderr file descriptors.
         close(STDIN_FILENO);
         close(STDOUT_FILENO);
         close(STDERR_FILENO);
         while(m_action());
     }	
 private:
     std::string m_path;
     std::string m_pidfile;
     Action m_action;
     // Action m_onExit;
};

Main function:

The PosixDaemon’s constructor takes the following parameters: the path where the daemon process will run, the path to PID file used to ensure that only a single instance is running and a lambda function which contains the code that will be in the daemon process.

std::random_device rdng;	
auto randomGen = std::bind(
        std::uniform_real_distribution<double>(10.0, 60.0),
        std::default_random_engine(rdng())
        );

setlogmask (LOG_UPTO (LOG_INFO));
openlog ("price-service", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);	

PosixDaemon daemon{		
    "/",
    "/tmp/price-server.pid",
    [&randomGen](){
      // Action executed in the child process (daemon)
      std::stringstream ss;
      ss << std::setprecision(3) << std::fixed;
      ss << "Price = " << randomGen() << " path = " << getcwd(nullptr, 0) ;
      syslog (LOG_INFO, "%s", ss.str().c_str());
      // 1 seconds delay
      std::this_thread::sleep_for(std::chrono::seconds(1));
      return true;
    }					  
};

daemon.run();

Compiling:

$ clang++ posix-daemon.cpp -o posix-daemon.bin -g -std=c++1z -Wall -Wextra && ./posix-daemon.bin

Running:

If there is already a process of this program running, it is killed and a new daemon is launched.

$ ./posix-daemon.bin
Process ID of child process = 6022
 [LOG] Kill process of PID = 4795
Child PID = 6022

See the daemon output with syslog:

$ journalctl -f -t price-service 

-- Logs begin at Wed 2018-10-03 16:00:02 -03. --
Nov 16 15:40:39 localhost.localdomain price-service[6022]: Price = 14.357 path = /
Nov 16 15:40:40 localhost.localdomain price-service[6022]: Price = 22.924 path = /
Nov 16 15:40:41 localhost.localdomain price-service[6022]: Price = 51.256 path = /
Nov 16 15:40:42 localhost.localdomain price-service[6022]: Price = 55.588 path = /
Nov 16 15:40:43 localhost.localdomain price-service[6022]: Price = 43.370 path = /
Nov 16 15:40:44 localhost.localdomain price-service[6022]: Price = 31.471 path = /
Nov 16 15:40:45 localhost.localdomain price-service[6022]: Price = 54.759 path = /
 ...  ...  ...  ...  ...  ...  ...  ...  ...

Stop daemon:

$ kill 6022

Posix - Socket/Server - telnet-like tool

This is a command line tool which can bind a server or client socket to a login shell, thus allowing remote access in a similar way to the old telnet protocol.

File: src/sample-programs/bsd-socket-shell.cpp
Gist: bsd-socket-shell.cpp

Modern C++ Features used:

Enum classes for modelling and handling socket errors.
C++11 auto keyword for functions, member functions and variables.
Lambda functions for handling daemon process, server’s client handling loop and so on.
=delete annotation for copy-constructor and copy-assignment operator.

Building:

$ clang++ bsd-socket-shell.cpp -o bsd-socket-shell.bin -lpthread -g -std=c++1z -Wall -Wextra

Show usage

$ ./bsd-socket-shell.bin 
Usage: 
: Success
 ./bsd-socket-shell.bin echo [port] [host]
 ./bsd-socket-shell.bin server [port] [host] [shell]
 ./bsd-socket-shell.bin client [port] [host] [shell]

Runnign as echo server:

Runing as server: Listen all addresses at port 9070

$ ./bsd-socket-shell.bin echo 9070 0.0.0.0
Running ECHO server.
 Waiting incoming connections ...: Success
 [TRACE] Connection received.: Success
line = hello world from server

line = testing server

line = 

line = new line to server

 [TRACE] Socket closed OK: Success
 [TRACE] Connection received.: Success

Client side: netcat.

$ rlwrap nc -v localhost 9070
Ncat: Version 7.60 ( https://nmap.org/ncat )
Ncat: Connection to ::1 failed: Connection refused.
Ncat: Trying next address...
Ncat: Connected to 127.0.0.1:9070.
=> Connected from: 127.0.0.1:56336
hello world from server
 => ECHO hello world from server
testing server
 => ECHO testing server

 => ECHO 
new line to server
 => ECHO new line to server


$ rlwrap nc -v localhost 9070
Ncat: Version 7.60 ( https://nmap.org/ncat )
Ncat: Connection to ::1 failed: Connection refused.
Ncat: Trying next address...
Ncat: Connected to 127.0.0.1:9070.
=> Connected from: 127.0.0.1:56340

Running as a telnet server for remote access

Server: bsd-socket-shell.bin
- When the server starts, the process is forked (copied) as a daemon process which can run even if the terminal is closed. Then, the initial process asks the user to hit return for stopping the daemon process.

$ ./bsd-socket-shell.bin server 9070 0.0.0.0 /bin/sh
 [LOG] Running daemon: Success
Process ID of child process = 17763
 [LOG] Daemon started OK.: Success
 ===> Enter RETURN for kill the daemon process or type CTRL+C to let it run.
 [TRACE] Running daemon - PID = 17763
 ===> Daemon stopped OK.

Client: netcat
- User types commands in the client side and they processed at the server side.

 $ rlwrap nc -v localhost 9070
 Ncat: Version 7.60 ( https://nmap.org/ncat )
 Ncat: Connection to ::1 failed: Connection refused.
 Ncat: Trying next address...
 Ncat: Connected to 127.0.0.1:9070.
 => Connected from: 127.0.0.1:56366

 pwd
 /
 uname -a
 Linux localhost.localdomain 4.16.3-301.fc28.x86_64 ... ....

 cd /etc

 whoami
 archbox

uptime
 05:31:23 up 1 day, 15:03,  1 user,  load average: 1.85, 1.68, 1.65

 # It is possible to connect and reconnect many times.
 $ rlwrap nc -v localhost 9070
 Ncat: Version 7.60 ( https://nmap.org/ncat )
 Ncat: Connection to ::1 failed: Connection refused.
 Ncat: Trying next address...
 Ncat: Connected to 127.0.0.1:9070.
 => Connected from: 127.0.0.1:56372

 pwd
 /
 ls
 bin
 boot
 dev
 etc
 home
 lib
 lib64
 lost+found
 media
 mnt

Running as a telnet server as client

Server: netcat
- User types command from this side.

$ rlwrap nc -v -l 0.0.0.0 9060
Ncat: Version 7.60 ( https://nmap.org/ncat )
Ncat: Generating a temporary 1024-bit RSA key. Use --ssl-key and --ssl-cert to use a permanent one.
Ncat: SHA-1 fingerprint: A753 5AC9 F6DF EC54 FE34 EF19 FC4B 02B7 79B5 BA30
Ncat: Listening on 0.0.0.0:9060
Ncat: Connection from 127.0.0.1.
Ncat: Connection from 127.0.0.1:57248.
=> Reverse shell connected from: 127.0.0.1:9060
whoami
archbox

pwd
/
free -m
              total        used        free      shared  buff/cache   available
Mem:          15931        7682         654         469        7594        7444
Swap:         19659           1       19658

which clang++
/usr/lib64/ccache/clang++

# Exit remote shell 
exit

# Connect again. 
$ rlwrap nc -l 0.0.0.0 9060
=> Reverse shell connected from: 127.0.0.1:9060
which clang++
/usr/lib64/ccache/clang++

Client: If the client-side terminal is closed or the user types CTRL+C, the client daemon process will keep running in background and trying to connect to the server, even if the server-side is shutdown.

$ ./bsd-socket-shell.bin client 9060 127.0.0.1 /bin/sh
Process ID of child process = 18231
 [LOG] Client daemon started OK.: Success
 ===> Enter RETURN for kill the daemon process or type CTRL+C to let it run.
 [TRACE] Running daemon - PID = 18231

Tool for inspecting binary file

Command line tool for inspectig binary files with the following features:

Identify files by magic number
Extract byte array at a given position.
Extract: 8 bits, 32 bits, 64 bits, integers signed or unsigned at given position.
File: src/sample-programs/binfo.cpp
Gist: binfo.cpp

Build:

$ clang++ binreader.cpp -o binreader.bin -g -std=c++1z -Wall -Wextra

Display usage:

$ ./binfo.bin 
Binary Info => Extract information from binary files.
Usage: ./binreader info       [FILE]
Usage: ./binreader get        [TYPE]  [OFFSET] [FILE]
Usage: ./binreader bytes-char [SIZE]  [OFFSET] [FILE]
Usage: ./binreader bytes-hex  [SIZE]  [OFFSET] [FILE]

Identify file formats by magic number (sequence of bytes in at the beginning).

$ ./binfo.bin info /usr/bin/bash
Maximum size = 16
.N/A =>  Unix Executable - ELF

 Bytes at 0x00 ==> 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 

$ ./binfo.bin info ~/account\ mind\ map.pdf 
Maximum size = 16
.pdf PDF - Portable Document File

 Bytes at 0x00 ==> 25 50 44 46 2d 31 2e 34 0a 25 c3 a4 c3 bc c3 b6 

$ ./binfo.bin info ~/Documents/logos/6904820-nasdaq-stock-market-new-york.jpg 
Maximum size = 16
JPEG Image - Extensions .jpg, .jpeg, .jpe, .jif, .jfif, .jfi

 Bytes at 0x00 ==> ff d8 ff e0 00 10 4a 46 49 46 00 01 02 01 01 2c

Show first 10 bytes of files as characters:

$ ./binfo.bin bytes-char 10 0x00 /usr/bin/bash
 RESULT ==> \0x7f E L F \0x02 \0x01 \0x01 \0x00 \0x00 \0x00 

$ ./binfo.bin bytes-char 10 0x00 ~/Fedora-Workstation-Live-x86_64-28-1.1.iso 
 RESULT ==> E R \0x08 \0x00 \0x00 \0x00 \0x90 \0x90 \0x00 \0x00

Extracting information at specific positions of a binary file (layout here ELF Format) Unix native executable.

“Magic number” identifying bytes 0x7F followed by ELF
- offset: 0x00
- 0x7F ELF (0x7F 0x45 0x4C 0x46)
e_ident[EI_OSABI] (size = 1 byte, offset = 0x07)
- contains the sytem ABI.
e_machine (size = 1 byte, offset = 0x12)
- Processor or instruction set.
e_entry (size = 8 bytes [64 bits], offfset = 0x18)
- Memory address of entry point where the process starts executing.

# Magic number 
$ ./binfo.bin bytes-char 4 0x00 /usr/bin/bash
 RESULT ==> \0x7f E L F 

$ ./binfo.bin bytes-hex 4 0x00 /usr/bin/bash
 RESULT ==> 7f 45 4c 46 

# System ABI => Result 0x00 or SystemV ABI 
$ ./binfo.bin get ui1 0x07 /usr/bin/bash
 RESULT ==> {hex = 0x0 ; dec = 0} 

# Processor architechture =>> 0x3E or x86-64 (64 bits)
$ ./binfo.bin get ui1 0x12 /usr/bin/bash
 RESULT ==> {hex = 0x3E ; dec = 62} 

# Entry point 
$ ./binfo.bin get ui8 0x18 /usr/bin/bash
 RESULT ==> {hex = 0x2E4B0 ; dec = 189616}

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Reverse Polish Notation Interpreter for math computation

Linux/Posix Daemon with syslog

Posix - Socket/Server - telnet-like tool

Tool for inspecting binary file

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Sample Modern C++ Programs

Sample Modern C++ Programs

Reverse Polish Notation Interpreter for math computation

Linux/Posix Daemon with syslog

Posix - Socket/Server - telnet-like tool

Tool for inspecting binary file