Can't create a digest with whirlpool

Question

I would like to create a whirlpool-digest with a program like this:

#include <openssl/evp.h>
#include <cstdio>

char sData[] = "test string";

int main(int argc, char *argv[]) {

    const EVP_MD *digest_type = EVP_whirlpool();
    EVP_MD_CTX   *mdctx       = EVP_MD_CTX_new();

    int res = EVP_DigestInit_ex(mdctx, digest_type, NULL);
    if (res == 1) {
        res = EVP_DigestUpdate(mdctx, (unsigned char *)sData, 12);
        if (res == 1) {
            unsigned char *pOut = (unsigned char *)OPENSSL_malloc(EVP_MD_size(digest_type));
            if (pOut != NULL) {
                unsigned int len = 0;
                res =  EVP_DigestFinal_ex(mdctx, pOut, &len);
                if (res == 1) {
                    for (int i = 0; i < len; i++) {
                        printf("%02x", pOut[i]);
                    }
                    printf("\n");
                } else {
                    printf("EVP_DigestFinal_ex() failed\n");
                }
            } else {
                printf("Couldn't allocate array\n");
            }
        } else{
            printf("EVP_DigestUpdate() failed\n");
        }
    } else {
        printf("EVP_DigestInit_ex() failed\n");
    }
    return 0;
}

When i run this, the call to EVP_DigestInit_ex() fails.

On the other hand, when i replace EVP_whirlpool() with EVP_sha512() in the above code, the program runs through and displays the digest.

Is there some particular parameter i have to pass to EVP_DigestInit_ex() to make this work?