Converting from String to Enum in C

Question

Is there a convienent way to take a string (input by user) and convert it to an Enumeration value? In this case, the string would be the name of the enumeration value, like

Answer 1

There isn't a direct way, but with C, you improvise. Here's an old trick. Purists may balk at this. But it's a way to manage this kind of stuff somewhat sanely. Uses some preprocessor tricks.

In constants.h put in the following:

CONSTANT(Sunday,  0)
CONSTANT(Monday,  1)
CONSTANT(Tuesday, 2)

In main.c:

#include 

#define CONSTANT(name, value) \
    name = value,

typedef enum {
    #include "constants.h"
} Constants;

#undef CONSTANT

#define CONSTANT(name, value) \
    #name,

char* constants[] = {
    #include "constants.h"
};  

Constants str2enum(char* name) {
    int ii;
    for (ii = 0; ii < sizeof(constants) / sizeof(constants[0]); ++ii) {
        if (!strcmp(name, constants[ii])) {
            return (Constants)ii;
        }   
    }   
    return (Constants)-1;
}   

int main() {
    printf("%s = %d\n", "Monday", str2enum("Monday"));
    printf("%s = %d\n", "Tuesday", str2enum("Tuesday"));
    return 0;
}

You can try other variations of the basic idea.