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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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