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Pieter
Pieter

Reputation: 32765

Can I display the value of an enum with printf()?

Is there a one-liner that lets me output the current value of an enum?

Upvotes: 60

Views: 163980

Answers (7)

Mateo de Mayo
Mateo de Mayo

Reputation: 939

Printing an enum value can be tricky as the sizes of each of its members can vary depending on the implementation. Take this example compiled on gcc 8.4.0.

#include <stdio.h>

int main(void) {
  enum option {A = 0, B = 0x100000000};
  enum option x = B;

  // Enumerator sizes of the same enumeration can differ
  printf("sizeof(A)=%zu\n", sizeof(A)); // sizeof(A)=4
  printf("sizeof(B)=%zu\n", sizeof(B)); // sizeof(B)=8
  printf("sizeof(x)=%zu\n", sizeof(x)); // sizeof(x)=8

  // Same output even though they have different values
  printf("A=%d\n", (int)A); // A=0
  printf("B=%d\n", (int)B); // B=0
  printf("x=%d\n", (int)x); // x=0

  // You should know beforehand the maximum enumerator size
  printf("A=%ld\n", (long)A); // A=0
  printf("B=%ld\n", (long)B); // B=4294967296
  printf("x=%ld\n", (long)x); // x=4294967296
}

Upvotes: 2

Alex Bondor
Alex Bondor

Reputation: 326

I had the same problem.

I had to print the color of the nodes where the color was: enum col { WHITE, GRAY, BLACK }; and the node: typedef struct Node { col color; };

I tried to print node->color with printf("%s\n", node->color); but all I got on the screen was (null)\n.

The answer bmargulies gave almost solved the problem.

So my final solution is:

static char *enumStrings[] = {"WHITE", "GRAY", "BLACK"};
printf("%s\n", enumStrings[node->color]);

Upvotes: 1

bmargulies
bmargulies

Reputation: 100050

As a string, no. As an integer, %d.

Unless you count:

static char* enumStrings[] = { /* filler 0's to get to the first value, */
                               "enum0", "enum1", 
                               /* filler for hole in the middle: ,0 */
                               "enum2", "enum3", .... };

...

printf("The value is %s\n", enumStrings[thevalue]);

This won't work for something like an enum of bit masks. At that point, you need a hash table or some other more elaborate data structure.

Upvotes: 54

BlueTrin
BlueTrin

Reputation: 10063

Some dude has come up with a smart preprocessor idea in this post

Easy way to use variables of enum types as string in C?

Upvotes: 3

DrAl
DrAl

Reputation: 72646

The correct answer to this has already been given: no, you can't give the name of an enum, only it's value.

Nevertheless, just for fun, this will give you an enum and a lookup-table all in one and give you a means of printing it by name:

main.c:

#include "Enum.h"

CreateEnum(
        EnumerationName,
        ENUMValue1,
        ENUMValue2,
        ENUMValue3);

int main(void)
{
    int i;
    EnumerationName EnumInstance = ENUMValue1;

    /* Prints "ENUMValue1" */
    PrintEnumValue(EnumerationName, EnumInstance);

    /* Prints:
     * ENUMValue1
     * ENUMValue2
     * ENUMValue3
     */
    for (i=0;i<3;i++)
    {
        PrintEnumValue(EnumerationName, i);
    }
    return 0;
}

Enum.h:

#include <stdio.h>
#include <string.h>

#ifdef NDEBUG
#define CreateEnum(name,...) \
    typedef enum \
    { \
        __VA_ARGS__ \
    } name;
#define PrintEnumValue(name,value)
#else
#define CreateEnum(name,...) \
    typedef enum \
    { \
        __VA_ARGS__ \
    } name; \
    const char Lookup##name[] = \
        #__VA_ARGS__;
#define PrintEnumValue(name, value) print_enum_value(Lookup##name, value)
void print_enum_value(const char *lookup, int value);
#endif

Enum.c

#include "Enum.h"

#ifndef NDEBUG
void print_enum_value(const char *lookup, int value)
{
    char *lookup_copy;
    int lookup_length;
    char *pch;

    lookup_length = strlen(lookup);
    lookup_copy = malloc((1+lookup_length)*sizeof(char));
    strcpy(lookup_copy, lookup);

    pch = strtok(lookup_copy," ,");
    while (pch != NULL)
    {
        if (value == 0)
        {
            printf("%s\n",pch);
            break;
        }
        else
        {
            pch = strtok(NULL, " ,.-");
            value--;
        }
    }

    free(lookup_copy);
}
#endif

Disclaimer: don't do this.

Upvotes: 6

anon
anon

Reputation: 

enum A { foo, bar } a;
a = foo;
printf( "%d", a );   // see comments below

Upvotes: 2

Matthieu
Matthieu

Reputation: 2761

enum MyEnum
{  A_ENUM_VALUE=0,
   B_ENUM_VALUE,
   C_ENUM_VALUE
};


int main()
{
 printf("My enum Value : %d\n", (int)C_ENUM_VALUE);
 return 0;
}

You have just to cast enum to int !
Output : My enum Value : 2

Upvotes: 31

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