Command Line Arguments Command Line Arguments Cmd.Line Args

What & Why?

space-separated strings behind program call
used to send information to a program when it starts
especially useful for automation/scripting

$ ls
$ rm *.txt
$ find -name *.jpg
$ g++ -o out xy.cpp

How To Access in C++ How To Access

`main.cpp`

#include <iostream>
int main (int const argc, char const*const* argv) {
  for (int i = 0; i < argc; ++i) {
    std::cout << argv[i] << '\n';
  }
}

$ g++ -o exe main.cpp
$ ./exe 12 abc -z 3
./exe
12
abc
-z
3

compile program 'exe'
run 'exe' with argsarguments
argv[0]  program call itself
argv[1]  1st argument
argv[2]
argv[3]
argv[4]

names argc and argv are only a convention
each element of argv is a C-string: a C-array of char
argv itself is a C-array of C-strings
argv[0] contains the program call (platform dependent)

Conversion to `std::string`, `int`, … Argument Conversion Conversion

#include <iostream>
int main (int const argc, char const*const* argv) {
  if (argc < 3) {
    std::cerr << "Usage:\\n " << argv[0]    << " <word> <times>\\n";
    return EXIT_FAILURE;
  }
  auto word  = std::string(argv[1]);
  int  times = atoi(argv[2]);
  for (int i = 0; i < times; ++i) {
    std::cout << word << ' ';
  }
  std::cout << '\n';
}

$ ./say
Usage: ./say <word> <times>
$ ./say ho! 3
ho! ho! ho!

execute without args
too few args ⇒ usage message
execute with args
program output

String → Number Conversion Functions String Conversions String Conversion

`#include <cstdlib>` (C-strings)

int    atoi  (char const*);
long   atoll (char const*);
double atof  (char const*);

`#include <string>` C++11

int    stoi (std::string const&);
long   stol (std::string const&);
float  stof (std::string const&);
double stod (std::string const&);

Command Line Argument Parsing Libraries Args Parsing Libraries Libraries

Library	CLI formats	opinions
Argument Aggregator	fixed	convoluted syntax hard to build complex CLIs
Argh!	arbitrary	minimalistic easy to use
argparse	fixed	C Library hard to build complex CLIs
Args	flexible	convoluted syntax hard to build complex CLIs
Argtable	fixed	C Library hard to build complex CLIs CLI defs are hard to read
Boost Program Options	flexible	mature supports config files C++98-era syntax & technical debt
CLI11	fixed	extensive feature set supports config files complex CLI defs are hard to read
CLIPP	arbitrary	relatively nice-looking, DSL-like syntax complex CLIs possible error handling could be better not very frequently updated
cxxopts	fixed	easy to write simple CLIs hard to build complex CLIs
DocOpt	fixed	great readability of CLI def. untyped CLI definition clumsy input querying
getopt	fixed	C Library convoluted syntax
getopt_long	fixed	C Library convoluted syntax
GFlags	fixed	convoluted syntax
TCLAP	flexible	convoluted syntax hard to build complex CLIs
The Lean Mean C++ Option Parser	fixed	truly convoluted syntax hard to build complex CLIs

Function Calls

Beginner's Guide / Input&Output

File I/O

Last updated: 2019-11-03

First Steps

Input & Output

Custom Types – Part 1

Diagnostics

Standard Library – Part 1

Function Objects

Standard Library – Part 2

Code Organization

Custom Types – Part 2

Generic Programming

Memory Management

Software Design Basics

Command Line Arguments Command Line Arguments Cmd.Line Args

What & Why?

How To Access in C++ How To Access

`main.cpp`

Conversion to `std::string`, `int`, … Argument Conversion Conversion

String → Number Conversion Functions String Conversions String Conversion

`#include <cstdlib>` (C-strings)

`#include <string>` C++11

Command Line Argument Parsing Libraries Args Parsing Libraries Libraries

Comments…

First Steps

Input & Output

Custom Types – Part 1

Diagnostics

Standard Library – Part 1

Function Objects

Standard Library – Part 2

Code Organization

Custom Types – Part 2

Generic Programming

Memory Management

Software Design Basics

What & Why?

How To Access in C++ How To Access

main.cpp

Conversion to std::string, int, … Argument Conversion Conversion

String → Number Conversion Functions String Conversions String Conversion

#include <cstdlib> (C-strings)

#include <string> C++11

Command Line Argument Parsing Libraries Args Parsing Libraries Libraries

Comments…

`main.cpp`

Conversion to `std::string`, `int`, … Argument Conversion Conversion

`#include <cstdlib>` (C-strings)

`#include <string>` C++11