HPR1330: Programming languages 3 - C

Hi, my name is Garjola and you are listening to a contribution to HPR. This is episode 3 of my programming language series and is entitled “Getting started with the C programming language”.

I am not going to teach you C, but just whet your appetite.

1 Intro

• What C is useful for
  • Systems programming
  • Number crunching
  • Graphics
  • Embedded systems
    • Arduino
• Advantages
  • speed
  • fine grained control of the memory management
  • close to the metal
  • the portable assembly language
• Drawbacks
  • fine grained control of the memory management
  • close to the metal
  • the portable assembly language

2 History of the language

• developed by Ken Thompson and Dennis Ritchie between 1969 and 1973 at AT&T Bell Labs.

• The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7 by Ritchie and Thompson, incorporating several ideas from colleagues. Eventually they decided to port the operating system to a PDP-11. B’s inability to take advantage of some of the PDP-11’s features, notably byte addressability, led to the development of an early version of C.

3 Uses

C is often used for “system programming”, including implementing operating systems and embedded system applications, due to a combination of desirable characteristics such as code portability and efficiency, ability to access specific hardware addresses, ability to pun types to match externally imposed data access requirements, and low run-time demand on system resources. C can also be used for website programming using CGI as a “gateway” for information between the Web application, the server, and the browser. Some reasons for choosing C over interpreted languages are its speed, stability, and near-universal availability.

One consequence of C’s wide availability and efficiency is that compilers, libraries, and interpreters of other programming languages are often implemented in C. The primary implementations of Python (CPython), Perl 5, and PHP are all written in C.

Due to its thin layer of abstraction and low overhead, C allows efficient implementations of algorithms and data structures, which is useful for programs that perform a lot of computations.

C is sometimes used as an intermediate language by implementations of other languages. This approach may be used for portability or convenience; by using C as an intermediate language, it is not necessary to develop machine-specific code generators.

C has also been widely used to implement end-user applications, but much of that development has shifted to newer languages.

4 Characteristics of the language

• imperative, compiled, static, weakly typed
• structured programming
  • Uses functions but it is not functional, but rather procedural
  • control flow if/else, for, while
  • curly braces, semi-colons
• all parameters are passed by value and references are simulated using pointers
• A program is a function called main

5 Tooling and environment

• editor
• compiler
  • makefiles for convenience, although higher level tools such as autoconf/automake or cmake exist
• debugger
• IDEs
• gnu tools for everything
  • emacs, pico, gedit, vi
  • gcc, clang
  • gnumake
  • gdb, xgdb, ddd
  • kdevelop

6 Hello World

#include <stdio.h>

int main(void) {
    printf("hello, world\n");
    return 0;
}

7 How to make a C program

• Write your main function into a file called myprogram.c
• compile your program
  • gcc -o myprogram myprogram.c
• if you use other libraries than C’s standard library, you will need to use a linker, like ld

Examples taken from An Introduction to GCC by Brian J. Gough, foreword by Richard M. Stallman

The classic example program for the C language is Hello World. Here is the source code for our version of the program:

#include <stdio.h>

int main (void) { printf ("Hello, world!\n"); return 0; }

We will assume that the source code is stored in a file called 'hello.c'.

To compile the file 'hello.c' with gcc, use the following command:

$ gcc -Wall hello.c -o hello

To run the program, type the path name of the executable like this:

$ ./hello
Hello, world!

8 Pointers!

C supports the use of pointers, a type of reference that records the address or location of an object or function in memory. Pointers can be dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-within-word field), but since a pointer’s type includes the type of the thing pointed to, expressions including pointers can be type-checked at compile time.

9 The standard library

• just use man!

On Unix-like systems, the authoritative documentation of the actually implemented API is provided in form of man pages. On most systems, man pages on standard library functions are in section 3; section 7 may contain some more generic pages on underlying concepts (e.g. man 7 math_error in Linux).

apropos sqrt | grep \(3\)

man 3 sqrt

man 3 qsort history

• the not-so-standard libraries
  • gsl
  • gtk
  • X

10 Languages of the C family

• C++, ObjectiveC, Java, C#, Go

11 Resources

• Learning GNU C by Ciaran O’Riordan.

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