C++ for Scientists - Technische Universität Dresden

48 CHAPTER 2. C++ BASICS
#ifndef athens foo hpp
#define athens foo hpp
double foo (double a, double b);
#endif
Note the ifndef and define C-preprocessor commands. These commands are called include guards
and prevent the file from being included several times. The use of such guards in header files is
quite common.
The source file in the library would be contained in the file foo.cpp.
#include ”foo.hpp”
double foo (double a, double b)
{ return a+b; }
The main program file is contained in the file bar.cpp:
#include
#include ”foo.hpp”
int main() {
double a = 2.1;
double b = 3.9;
std::cout ≪ foo(a,b) ≪ std::endl ;
}
Include files usually contain the interface of software packages and are stored somewhere on
disk. The compiler is told where to look for the include files. The programmer can partially
control this as follows:
• #include ”foo.hpp”: the compiler looks in the directory of the including file and the list of
directories it is given.
• #include : the compiler only looks in the list of directories it is given.
Frequently used include files
The types and functions defined in the following include files are in the namespace std.
• : input and output stream, e.g. std::cin and std::cout
• : file input and output
• : For assertions, see §2.6.5.
• : Headers for the C functions from math.h, among others: abs, fabs, pow, acos,
asin, atan, atan2, ceil, floor, cos, cosh, sin, sinh, exp, fmod (floating point mod), modf (split in
integer and fractional part (< 1)), log, log10, sqrt, tan, tanh
And other useful functions such as isnan.
• : String operations