1. Miscellaneous C++ Topics
Professor Hugh C. Lauer CS-2303, System Programming Concepts
(Slides include materials from The C Programming Language, 2nd edition, by Kernighan and Ritchie, Absolute C++, by Walter Savitch, The C++ Programming Language, Special Edition, by Bjarne Stroustrup, and from C: How to Program, 5th and 6th editions, by Deitel and Deitel)
CS-2303, A-Term 2012
Miscellaneous C++ Topics

2. Miscellaneous C++ Topics
Outline
A note on Preprocessor Wrappers
Inline functions
Default Arguments
Function Templates
CS-2303, A-Term 2012
Miscellaneous C++ Topics

3. Preprocessor Wrappers
Exactly as in C
Prevent code from being included more than once.
#ifndef – “if not defined”
Skip this code if it has been included already
#define
Define a name so this code will not be included again
#endif
If the header has been included previously
Name is defined already and the header file is not included again.
Prevents multiple-definition errors
Example
#ifndef TIME_H #define TIME_H … // code #endif
§A12.5 in K&R (Not in Absolute C++)
CS-2303, A-Term 2012
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4. Miscellaneous C++ Topics
Inline Functions
Advice to compiler that the body of the function may be substituted for a call to that function
Insert the qualifier inline before return type of function
Example:–
inline int max(int a, int b) { return (a>b) ? a : b; }
§7.2 of Absolute C++
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Miscellaneous C++ Topics

5. Inline Functions (continued)
Reasons:–
Reduce function call overhead—especially for small functions in inner loops
Takes advantage of compiler’s local optimizations
Trade-off of inline functions
Multiple copies of the function code are inserted in the program (possibly making the program larger)
The compiler may ignore the inline qualifier
Typically does so for all but the smallest functions
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Miscellaneous C++ Topics

6. Inline Function Example
inline qualifier
Complete function definition so compiler knows how to expand a cube function call into inline code
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7. Inline Functions (continued)
Typical usage:– Member function of a class
Very simple, short, fast operations
Especially in inner loops
Especially set and get functions
Saves the (non-trivial) overhead of invoking a method, creating activation record, etc.
Encourages cleaner, more readable code
inline qualifier is strictly advisory
Widely used whenever you ask yourself about efficiency of a calling a function vs. accessing a class member directly
CS-2303, A-Term 2012
Miscellaneous C++ Topics

8. Miscellaneous C++ Topics
Questions?
CS-2303, A-Term 2012
Miscellaneous C++ Topics

9. Miscellaneous C++ Topics
Default Argument
Definition:– A default value to be passed to a parameter
When the function/method call does not specify an argument for that parameter
Example
void prnt(int value, int base = 10); …
prnt(100); //prints in base 10
prnt(100,16); //prints in base 16
prnt(100,8); //prints in base 8
prnt(100,3); //prints in base 3
An “assignment” as part of parameter list
CS-2303, A-Term 2012
Miscellaneous C++ Topics

10. Default Arguments (continued)
Must be rightmost parameter(s) in parameter list of function
Default value specified in function prototype
Usually in class header file
So compiler knows how to compile calls
If one argument is defaulted, all arguments to right of it must be defaulted also
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11. Default Argument Example
void f(int a, double b, int c = 10, bool d = false); f(100, 3.14) // okay f(100, 3.14, 15) // okay f(100, 3.14, 15, true) // okay f(100, 3.14, , true) // no good f(100, 3.14, 10, true) // okay
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12. Summary – Default Arguments
Simplest form of function overloading
Default values specified in header and function prototype
Defaults applied from right to left
§4.2, Absolute C++ (Near end of section)
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Miscellaneous C++ Topics

13. Miscellaneous C++ Topics
Questions?
CS-2303, A-Term 2012
Miscellaneous C++ Topics

14. Miscellaneous C++ Topics
Problem
What about the case when all of the overloaded functions have essentially the same code, but for different types
Not good style to write a bunch of nearly identical code
Inefficient of programmer time
Various instances can get out of sync with each other
Some cases might be missed
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Miscellaneous C++ Topics

15. Solution – Function Templates
A more compact and convenient form of overloading.
Identical program logic and operations for each data type
§16.1 of Absolute C++
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16. Miscellaneous C++ Topics
Function Template
Written by programmer once
Essentially defines a whole family of overloaded functions
Begins with the template keyword
Contains a template parameter list of formal type and the parameters for the function template are enclosed in angle brackets (<>)
Formal type parameters
Preceded by keyword typename or keyword class
Placeholders for fundamental types or user-defined types
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17. Function Template Example
Using formal type parameter T in place of data type
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18. Miscellaneous C++ Topics
Result
Whole Family of Overloaded Functions
All with the “same” source code
All doing the same thing, but with different data types
Defined in one place
Common Programming Errors
Not placing keyword class or keyword typename before every formal type parameter of a function template
Writing < class S, T > instead of < class S, class T > ) is a syntax error
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19. Miscellaneous C++ Topics
Definition:–
Specialization
The automatic generation of a new “overloaded function” from the template as needed
I.e., whenever a function template is called with a particular type
Example for function template max with type parameter T called with int arguments
Compiler detects a max invocation in the program code.
int is substituted for T throughout the template definition.
This produces function-template specialization max<int>
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Miscellaneous C++ Topics

20. Specialization Example
Compiler:–
Suspends what it was doing
Generates a new overloaded function from template maximum for type parameter int
Compiles this new function
Returns to this program and compiles a call to new function
Invoking maximum with int arguments
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21. Specialization Example (continued)
Invoking maximum with double arguments
Compiler does same again, but for parameter type double
Invoking maximum with char arguments
And again, but for parameter type char
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22. Specialization (continued)
Each time that the compiler encounters a use of maximum with a type that it has not seen before
… it creates a new instance of the function maximum with new parameter types
With new mangled name!
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23. Function Templates Summary
Very important for
Code readability
Code reuse
Good coding style
Programmer efficiency
Foundation of other template features in C++
CS-2303, A-Term 2012
Miscellaneous C++ Topics

24. Miscellaneous C++ Topics
Questions?
CS-2303, A-Term 2012
Miscellaneous C++ Topics