CS 509 Class Notes

Lecture Notes for Advanced Programming II

Part of standard C and C++.
- Part of the standard preprocessor.
- "Preprocessor" means "precompilation".
- The g++ and CC -E option runs your code through the preprocessor and nothing else.
Include statement syntax is not C++ syntax.
#include "include-file-name"
#include <include-file-name>
< > and "" have different search paths.
- < > usually searches only the system directories.
- " " searches other directories first, then system directories.
  - For example, " " searches . (the current directory).
  - This depends on the compiler.

The -I compiler command-line option manipulates the " " search paths.
- Does not effect the < > search paths.
- Available for g++ and CC.
For example: g++ -Imylib ...
- Search ./mylib, then ., then, ...
-I options are cumulative.
- g++ -Iliba -Ilibb ... searches liba, then libb then ...
Some compilers support options to influence the < > search path too.
- The g++ support for this is too ugly to talk about.

Includes implement textual inclusion.
- The contents of the include file replaces the include statement.
- This causes code and variable duplication, not sharing.
- Not like packages in ada or java.
Textual inclusion can cause problems.
- Large source files.
- Circular includes.
- Duplicate code.

Learn and use the #ifndef idiom for include files.

#ifndef _includefile_h_
#define _includefile_h_

// Included material here.

#endif

Standard include files need standard names.
- Many pre-standard extensions; .h, .hh, .H, .hxx
The standard eliminated the extension.
- C++ and C standard include files have no extensions - no .h
- Some compilers may still accept .h standard includes.
  - Don't use it; it's nonstandard.
It usually doesn't mater, but sometimes it does.
- <string> is not <string.h> is not <cstring>
Other include filenames can be arbitrary.
- Filenames can include local conventions; / vs. \.
- Watch out for portability.

The C++ and C standard includes define names inside the std namespace.
- Names should be prefixed with std::.
- using declarations make this less cumbersome.
- However, std:: is useful documentation.
  - Now where did that come from?
Compilers respect this to varying degrees.
- Don't rely on a compiler's particular treatment.
- Use std:: or explicitly eliminate it.
Avoid subverting namespaces in include files.
- It may cause unintentional name clashes in the including file's code.
- Include files should be good guests.
- Be especially careful of using namespace.

There are somewhere around 50 standard include files.
Stream IO include files.
- <iostream>, <iomanip>, <fstream>
STL include files.
- <vector>, <list>, <map>, <iterator>, <algorithm>, <utility>, <queue>, <stack>, <deque>, <set>, <bitset>, <functional>, <memory>
Exception include files.
- <exception>, <stdexcept>
String include files.
- <string>, <sstream>
- But not <strstream> (it's deprecated).
Odds and ends.
- <locale>, <limits>, <typeinfo>

C defines a set of standard include files too.
- These are available for use in C++.
- From C++, they are part of the std namespace, sometimes.
  - It depends on the compiler.
  - Macros are not part of a namespace.
Access them using C++ include conventions.
- Drop the .h and prepend a 'c'.
- For example, given the C include assert.h, use
```
#include <cassert>
```
- Accessing the .h forms from C++ is nonstandard.
- c-prepended headers make the proper C++ extern declarations, .h headers do not.

Assert macros in <cassert>.
```
assert((0 <= i) and (i < N));
```
assert()'s a macro, no std::.
Character functions in <cctype>.
```
ch = std::toupper(ch);
```
Math functions in <cmath>.
```
double x = std::log(M_PI);
```
M_PI is a macro, log() is a function; std::M_PI doesn't compile.
System-dependent limits in <climits>.
```
cout << "Biggest int is " << INT_MAX << "\n"
```
std::INT_MAX doesn't compile either.
Time utilities in <ctime>.

Any other include files are non-standard.
- strcasecmp(), strings.h, X Window System includes.
- Filename syntax is arbitrary.
- These are non-standard, potentially non-portable features.
"non-standard" is not bad - "unconventional" is bad
- Gratuitously non-standard is bad too.
Don't #include source (.cc) files, but the STL does.
- Usually considered a hostile act.
- Templates are excused from this convention.

Include statements implement textual inclusion.
- Big code, infinite includes.
Become familiar with the standard C and C++ include files.
- Reduce your work, improve code (and your) portability.
C++ standard includes have no extensions.
- C standard includes in C++ have a c prefix too.
- Non-standard includes have whatever.
Learn and follow the include conventions.
- Don't include source, don't subvert namespaces.
- Learn the local conventions too.

This page last modified on 22 January 2003.