comp.lang.c FAQ list · Question 20.1

Q: How can I return multiple values from a function?

A: There are several ways of doing this. (These examples show hypothetical polar-to-rectangular coordinate conversion functions, which must return both an x and a y coordinate.)

1. Pass pointers to several locations which the function can fill in:

   #include <math.h>
   
   polar_to_rectangular(double rho, double theta,
   		double *xp, double *yp)
   {
   	*xp = rho * cos(theta);
   	*yp = rho * sin(theta);
   }
   
   ...
   
   	double x, y;
   	polar_to_rectangular(1., 3.14, &x, &y);
   

2. Have the function return a structure containing the desired values:

   struct xycoord { double x, y; };
   
   struct xycoord
   polar_to_rectangular(double rho, double theta)
   {
   	struct xycoord ret;
   	ret.x = rho * cos(theta);
   	ret.y = rho * sin(theta);
   	return ret;
   }
   
   ...
   
   	struct xycoord c = polar_to_rectangular(1., 3.14);
   

3. Use a hybrid: have the function accept a pointer to a structure, which it fills in:

   polar_to_rectangular(double rho, double theta,
   		struct xycoord *cp)
   {
   	cp->x = rho * cos(theta);
   	cp->y = rho * sin(theta);
   }
   
   ...
   
   	struct xycoord c;
   	polar_to_rectangular(1., 3.14, &c);
   

   (Another example of this technique is the Unix system call stat.)
4. In a pinch, you could theoretically use global variables (though this is rarely a good idea).

See also questions 2.7, 4.8, and 7.5a.

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