SSL signature verrification cross language issue - c++

Question

I have the following code in an C websocket server application I have. The code performs ssl signature verification on a message with a given public key. The code works fine in the C application, but recently I started writing it on c++.The issue I encountered is that the same code, that is below, is in both applications, without change, both times receiving the same input data, but the one compiled with c++ yields SSL error bad signature.
Here is the code:
int verifyMessageSignature(const char* decoded_message, int pos,
unsigned char* signature, char* publicKey)
{
SSL_library_init();
SSL_load_error_strings();
ERR_load_BIO_strings();
// OpenSSL_add_all_algorithms()
if (!publicKey)
{
printf("publicKey is null\n");
}
BIO* keyBio = BIO_new_mem_buf(publicKey, -1);
if(!keyBio)
{
printf("failed to created BIO\n");
printError(ERR_get_error());
}
BIO_set_mem_eof_return(keyBio, 0);
RSA* rsa = PEM_read_bio_RSA_PUBKEY(keyBio, NULL, NULL, NULL);
if (!rsa)
{
printf("Error in PEM_read_bio_RSA_PUBKEY\n");
printError(ERR_get_error());
}
EVP_MD_CTX *mdctx = NULL;
if (!(mdctx = EVP_MD_CTX_create()))
{
printf("Error in ctx\n");
printError(ERR_get_error());
}
EVP_PKEY* pk = EVP_PKEY_new();
if (EVP_PKEY_set1_RSA(pk, rsa) != 1)
{
printf("err in EVP_PKEY_set1_RSA\n");
printError(ERR_get_error());
}
if (EVP_DigestVerifyInit(mdctx, NULL, EVP_sha1(), NULL, pk) != 1)
{
printf("error in EVP_DigestVerifyInit\n");
printError(ERR_get_error());
}
if (EVP_DigestVerifyUpdate(mdctx, decoded_message, pos) != 1)
{
printf("error in EVP_DigestVerifyUpdate\n");
printError(ERR_get_error());
}
if (EVP_DigestVerifyFinal(mdctx, signature, 512) == 1)
{
/* Success */
printf("Successful verification!\n");
}
else
{
/* Failure */
printf("Unsuccessful verification!\n");
printError(ERR_get_error());
BIO_free_all(keyBio);
RSA_free(rsa);
EVP_PKEY_free(pk);
EVP_MD_CTX_destroy(mdctx);
ERR_free_strings();
return 1;
}
BIO_free_all(keyBio);
RSA_free(rsa);
EVP_PKEY_free(pk);
EVP_MD_CTX_destroy(mdctx);
ERR_free_strings();
return 0;
}
This code works fine in C. it successfully verifies the signature in my tests, whilst the same code, with the same input data (keys, messages, etc..) in c++ yields bad signature.
I am compiling under Ubuntu, using gcc and g++ (latest)
What could be causing this issue?

Answer 1

Solved. The issue was that i was using std::string to pass the decoded message around, which somehow was fucking it up. I switched the c++ code to use also char* strings for this section and is fine now.
Thanks for the replies, I hope someone else finds this useful.
Edit:
PS: I am using another function for generating the decoded message itself. Usage of std::string there was causing this issue.