- The document discusses different approaches for copying strings in C, including strcpy, strncpy, strlcpy, and strcpy_s. - strcpy can cause buffer overflows if the destination is too small, while strncpy does not guarantee a properly terminated string. - strlcpy aims to prevent overflows and ensure valid strings, but may truncate and requires external libraries. - strcpy_s from C11 solves the problems of previous functions and is part of the standard, but support is limited.

1. Not Your Fathers C
C Application Development In 2016

2. Introduction
About Me
● Living in Leipzig
● five years of exploring ways to write high
level C
● C and me is a „convenience marriage“
(Zweck Ehe)
● Other tech stuff: Python, Java
● http://blog.toepfer.nu

3. Introduction
Leipzig Softwerkskammer
● Software Craftsmanship Community in
Leipzig
● Once a month
● Mix of coding and beer
● https://www.softwerkskammer.org/groups/
sachsen

4. Introduction
My C Scope
● Application development in a legacy
system
● No embedded software
● I am not a kernel hacker

5. Introduction
Why Still C
● Legacy Code
● Embedded systems
● Speed
● Direct Memory Control (Garbage Collection
can be slow!)

6. A Punk Rock Language
[1]

7. A Punk Rock Language
Essay in PragProg Magazine
March 2011
[2]

8. A Punk Rock Language
1978
● Book release and first peak of Punk Rock
[4][3]

9. A Punk Rock Language
Three Chords Is Enough To
Form A Band
[5]

10. A Punk Rock Language
Three Basic Data Types In C
[6]

11. A Punk Rock Language
The Craftsman's Question
C is quirky, flawed, and an enormous
success.. (Dennis Ritchie On C)
[7]
How To Deal
With A Punk Rock
Language?

12. Structure

13. Structure
“On Information Hiding”
● „On the criteria to be used in decomposing
systems into modules”, CACM, Dec., 1972
by David L. Parnas.
● Bottom line: Modularization is a very old
concept

14. Structure
A C Module
● A *.c file is called a “module”
● Should contain related functions and data
● How to design related functions and data –
can't we have classes?

15. Structure
What Is A Class
● A bunch of functions working on (mainly)
the same variables. (Uncle Bob)
● That's exactly what we have – how to
implement this in C?

16. Structure
Main OO Structure Elements
● Classes – defines an object
● Methods – actions on the object's data
● Packages – organizing classes

17. Structure
A Python Example
from long.package.path.my_class import MyClass
...
my_instance = MyClass()
print(my_instance.say_hello())

18. Structure
Objects in C
● Only function names in global name space
● We need to use a naming convention for
structuring:
– Class name
– Underscore
– Method name

19. Structure
Naming Example
● The Module name: MyClass.c
● Functions inside:
– The constructor: MyClass_create()
– A method: MyClass_sayHello()
– The destructor: MyClass_destroy()

20. Structure
Example Ported To C
#include "MyClass.h"
...
MyClass *my_instance = MyClass_create();
printf("%sn", MyClass_sayHello(my_instance));
MyClass_destroy(my_instance);

21. Structure
Objects in C
● C can give you Object Orientation –
Without Inheritance
● It's no real OO – I just call it „Objects in C“
● Not to be mistaken with *.o files which are
compiler result files

22. Structure
Objects In C - My Rules
● treat a C module as a class
● all public functions of that file are the methods of
the class
● the first part of the function name is the name of
the class
● the second part of the function name is the name
of the method
● The first argument of the function is the instance
of the object

23. Structure
No Hard Rules
● A module can be designed as an object – but
it doesn't have to – simply related functions
are still ok.
● I prefer camel case for class and method
names but there are other ways as well (see
next example).
● As with every convention:
– define your rules and stick to it
– it's not a religion

24. Structure
Pebble Smart Watch
● Smart watch which started as crowd
funding campaign
[8]

25. Structure
„Hello Pebble“
Window *window;
TextLayer *text_layer;
void init() {
window = window_create();
text_layer = text_layer_create(GRect(0, 0, 144, 40));
text_layer_set_text(text_layer, "Hello, Pebble!");
layer_add_child(window_get_root_layer(window),
text_layer_get_layer(text_layer));
window_stack_push(window, true);
}
void deinit() {
text_layer_destroy(text_layer);
window_destroy(window);
}
int main() {
init();
app_event_loop();
deinit();
return 0;
}

26. Abstraction

27. Abstraction
An Old Idea
Taken from „The Structure And Interpretation Of
Computer Programs“, 2nd Edition, MIT Press, 1996

28. Abstraction
The Standards
● ANSI standard (Strings, Math, Memory)
● Is enhanced by the Posix Standard
(Sockets, File descriptors...)
● Covers the bare minimum
● “1000” string functions and non is the right
one

29. Abstraction
What I Expect
● Lists
● Hashtable/ Associative Array/ Dictionary
● Painless Strings
● …
● Basically: Not Re-Inventing The Wheel
Every Time

30. Abstraction
GLib2
● https://developer.gnome.org/glib/
● Initially developed by GNOME but
separated GTK+ to be used in other
software
● Not to be mistaken with glibc (GNU
Implementation of the ANSI and Posix
Standards)

31. Abstraction
GLib2
● „the missing standard library“
● „Boost for C“
● In my opinion the best universal purpose
library for C – but there are others as well
(Apache)

32. Abstraction
GLib2 List Example
GList *beers = NULL;
beers = g_list_append(beers, g_strdup("Helles"));
beers = g_list_append(beers, g_strdup("Pils"));
beers = g_list_append(beers, g_strdup("Weizen"));
printf("I know %i beers.n", g_list_length(beers));
printf("The third beer is a %s.n",
(char*)g_list_nth_data(beers, 2));
GList *iterator = beers;
puts("All beers:");
while (iterator != NULL) {
printf("%sn", (char*)iterator->data);
iterator = g_list_next(iterator);
}
g_list_free_full(beers, free);

33. Error Handling

34. Error Handling
Back To The Basics
● No fancy stuff like try / catch blocks and
exceptions
● Has to be done manually
● There is a third state: undefined

35. Error Handling
Classic Via Return Code
int doCalculations()
{
int rc = calcSomething();
if (rc != OK)
{
printf("function calcSomething had an error.n");
return NOT_OK;
}
rc = calcSomethingElse();
if (rc != OK)
{
printf("function calcSomethingElse had an error.n");
return NOT_OK;
}
return OK;
}

36. Error Handling
A Case For goto
int doCalculations()
{
int rc = calcSomething();
if (rc != OK) goto error_calcSomething;
rc = calcSomethingElse();
if (rc != OK) goto error_calcSomethingElse;
return OK;
// error handling
error_calcSomething:
printf("function calcSomething had an error.n");
return NOT_OK;
error_calcSomethingElse:
printf("function calcSomethingElse had an error.n");
return NOT_OK;
}

37. Error Handling
A Case For goto
● Only use it for local error handling & clean
up
● The rule: “Jump forward in a function”
● No replacement for „continue“ and „break“
in loops

38. Error Handling
An empirical study of goto in C code
● University study published in 2015 *
● Analysis of all C code at github.com
– 2 million lines of Code
– 11 000 repositories
● Result
– 80 % use goto for error handling
– 40% use it for resource clean up
* https://peerj.com/preprints/826v1/

39. Error Handling
Conclusion of the Study
We conclude that developers limit
themselves to using goto appropriately in
most cases, and not in an unrestricted
manner like Dijkstra feared, thus
suggesting that goto does not appear to be
harmful in practice.

40. Testing

41. Testing
Unit Testing Is Universal
● “self testing code” is of course possible in
C as well
● Requires good understanding of the code >
compile > link > execute cycle
● many unit testing frameworks are available,
popular are:
– CppuTest
– googletest

42. Testing
A Futter Machine

43. Testing
The Big Picture

44. Testing
Test First

45. Testing
No Such Function
machine_test.c:9:5: warning: implicit declaration of function
‘Machine_create’ [-Wimplicit-function-declaration]
rc = Machine_create();
^
/tmp/ccThL6ze.o: In function `create_ok':
machine_test.c:(.text+0x15): undefined reference to `Machine_create'
collect2: error: ld returned 1 exit status
● one warning and one error:
– Compiler: Unknown function, auto-detecting prototype
missing
– Linker: Implementation missing

46. Testing
Provide The Interface

47. Testing
Implementation Still Missing
/tmp/ccOl0iLr.o: In function
`test_create_machine_with_no_error':
machine_test.c:(.text+0x15): undefined reference to
`Machine_create'
collect2: error: ld returned 1 exit status
● linker still complaining about missing
implementation

48. Testing
Provide A Simple Implementation

49. Testing
The Test Passes
● Now everything required is present:
– Test (our mini application)
– Interface (the header file)
– Implementation (the machine.c file)

50. Testing
The Big Picture Revisted

51. Old Friends

52. Old Friends
Function Pointer
● Define the code to be executed at runtime
● “Typed functional programming”
● “registering a callback” – that’s a function
pointer
● Awkward syntax but very useful

53. Old Friends
Function Pointer Example
// calc functions
int addInt(int a, int b) {return a + b;}
int multiplyInt(int a, int b) {return a * b;}
int calcInt(int a, int b, int (*calcFunction)(int,int)) {
return calcFunction(a, b);
}
int main(void) {
int sum = calcInt(2, 3, addInt);
int product = calcInt(2, 3, multiplyInt);
printf("Sum is %i, product is %in", sum, product);
}

54. Old Friends
Language Bridges
● Integrate C code in other programming
language
● Develop “high level” and fall back when
– Using existing C library
– CPU cycles matter
– …
● More likely at application edges than core

55. Old Friends
Bridging from Python To C (ctypes)
int add(int a, int b) {
return a + b;
}
C function in libmaikmath.so:
import ctypes
mylib = ctypes.cdll.LoadLibrary('libmaikmath.so')
print('1 + 2 =', mylib.add(1, 2))
Using “add” in a Python program:
Warning: Oversimplified

56. How To Code

57. How To Code
My Conventions
● Code for the programmer after me - not the
machine
● Rarely use Macros - adds one more
indirection in my head
● Try to keep it plain C pimped with modern
libraries - but not a new language
(GObject/ GTK, libcello)

58. How To Code
I Like IDEs
● My setup:
– Eclipse CDT with
– VIM plugin and
– Running on Linux in a Vagrant provided Virtualbox
– Windows 7 Host
● JetBrains CLion looks promising
● My next try: Visual Studio Code
with C/ C++ plugin

59. How To Code
Eclipse CDT Example

60. Further Reading

61. Further Reading
Getting Started
[9]

62. Further Reading
Structure
[10]

63. Further Reading
Syntax
[11]

64. Further Reading
Online
● Nice Primer:
http://developer.getpebble.com/tutorials/be
ginner/primer
● How To C in 2016 – good discussion:
https://matt.sh/howto-c
● My collection of C tips:
http://we-press-buttons.blogspot.de/search/
label/C

65. Thank You For Your Attention
[12]

66. Image References
● [1] - http://www.bilbaoisrock.com/wp-content/uploads/2013/04/the-ramones.jpg
● [2] - https://pragprog.com/magazines/2011-03/punk-rock-languages
● [3] -
https://upload.wikimedia.org/wikipedia/commons/thumb/9/95/The_C_Programming_Language,_First_Edition_Cover_
(2).svg/2000px-
The_C_Programming_Language,_First_Edition_Cover_(2).svg.png
● [4] - https://ryebreadrodeo.com/prodimages/cz117.jpg
● [5] - http://blog.sharemyguitar.com/wp-content/uploads/2012/03/SMG-Power-Chord.jpg
● [6] - http://codingfox.com/wp-content/uploads/2013/08/data-types.gif
● [7] - https://upload.wikimedia.org/wikipedia/commons/2/26/Card_reader_segfault.jpg
● [8] - http://cdn.mos.techradar.com/art/Watches/Pebble/Pebble%202/Time_2_Collection-970-80.jpg
● [9] - http://ecx.images-amazon.com/images/I/41%2BbFKtFHjL._SX405_BO1,204,203,200_.jpg
● [10] - https://imagery.pragprog.com/products/173/jgade.jpg?1298589886
● [11] - http://ecx.images-amazon.com/images/I/51Rs4gK05iL._SX379_BO1,204,203,200_.jpg
● [12] - http://agilebacon.com/wp-content/uploads/2014/07/exhausted-student-with-laptop.jpg

67. Backup

68. Abstraction
String Copy Tour
● Scenario
– Copy a string to a new string
– The memory for the new string is smaller than
the original one

69. Abstraction
Strings In C
● NUL (‘0’) terminated array of single bytes
● Example:
char source[] = "abcde";
a b c d e ?? 0

70. Abstraction
String Copy with strcpy
● First appeared 1975
● Bells/ AT&T: Programmer's Workbench
(PWB/UNIX)
● Renowned for Buffer Overflows

71. Abstraction
strcpy Example
char source[] = "abcde";
char destination[4] = {0};
0 0 0 0 ?? ????
Content of “destination”:
strcpy(destination, source);
Buffer Overflow
a b c d ?? ??0e
Content of “destination”:

72. Abstraction
String Copy with strncpy
● First appeared 1979
● AT&T Unix Version 7
● Found wider usage in the 1990ies to
overcome strcpy problems
● Problem: Does not guarantee a proper C
string as result.

73. Abstraction
strncpy Example
char source[] = "abcde";
char destination[4] = {0};
0 0 0 0 ?? ????
Content of “destination”:
strncpy(destination, source,
sizeof(destination));
No NUL
byte
??a b c d? ???
Content of “destination”:
Next usage of “destination” will read
these bytes until NUL is found.

74. Abstraction
String Copy with strlcpy
● First appeared 1998 (OpenBSD)
● Aim:
– No buffer overflows
– Produce always valid C Strings (NUL terminated)
● Problems:
– Truncates strings (controversial)
– No adoption into standards
– Third party libs required

75. Abstraction
strlcpy Example
char source[] = "abcde";
char destination[4] = {0};
0 0 0 0 ?? ????
Content of “destination”:
strlcpy(destination, source,
sizeof(destination));
String content is incomplete
??a b c 0? ???
Content of “destination”:

76. Abstraction
String Copy with strcpy_s
● First appeared 2003 (Microsoft)
● Solves the previous problems
● Is part of C11 standard (optional appendix)
● Currently only available as third party
library
– “Safe C” by Cisco
– https://sourceforge.net/projects/safeclib/

77. Abstraction
strcpy_s Example
char source[] = "abcde";
char destination[4] = {0};
0 0 0 0 ?? ????
Content of “destination”:
??0 0 0 0? ???
Content of “destination”:
errno_t result = strcpy_s(destination,
sizeof(destination), source);ESLEMAX (length exceeds max)

78. Abstraction
Alternative String Copy Approaches
● Heap based
● Memory allocation automatically
● Must be freed manually
● Must be checked if successful

79. Abstraction
Alternative String Copy Approaches
● asprintf
– GNU extension of C standard
– Part of glibc
● GLib Strings
– Part of Glib
– Object like behaviour
– Offers functions like “append”, “up”, “down”…
● ...