Double free or corruption C++ Avro - c++

Question

I need to serialize a JSON string using Avro in C++.
I installed the libserdes library (https://github.com/confluentinc/libserdes) and I used the example code
./examples/kafka-serdes-avro-console-producer.cpp
to write a main,
which serializes a JSON string as follows.
{"s":"BTCUSDT","c":"spread","u":123456789,"a":20000.4,"b":21000.5,"A":1.25,"B":0.58,"p":-1,"P":-1,"st":-1,"rt":1675000000123000}
Here is the code
#include "fh_price_t.h"
#include "avro/Encoder.hh"
#include "avro/Decoder.hh"
#include <avro/Generic.hh>
#include <avro/Specific.hh>
#include <avro/Exception.hh>
#include "libserdes/serdescpp-avro.h"
#include <iostream>
#include <sstream>
#include <string>
#include <fstream>
#define FATAL(reason...) do { \
std::cerr << "% FATAL: " << reason << std::endl; \
exit(1); \
} while (0)
template<class T> std::string to_string_a (const T& x) {
std::ostringstream oss;
oss << x;
return oss.str();
}
/**
* Convert JSON to Avro Datum.
*
* Returns 0 on success or -1 on failure.
*/
int json2avro (Serdes::Schema *schema, const std::string &json,
avro::GenericDatum **datump) {
avro::ValidSchema *avro_schema = schema->object();
/* Input stream from json string */
std::istringstream iss(json);
auto json_is = avro::istreamInputStream(iss);
/* JSON decoder */
avro::DecoderPtr json_decoder = avro::jsonDecoder(*avro_schema);
avro::GenericDatum *datum = new avro::GenericDatum(*avro_schema);
try {
/* Decode JSON to Avro datum */
json_decoder->init(*json_is);
avro::decode(*json_decoder, *datum);
} catch (const avro::Exception &e) {
std::cerr << "% JSON to Avro transformation failed: "
<< e.what() << std::endl;
return -1;
}
*datump = datum;
}
int main (int argc, char* argv) {
izycoinstestavro::fh_price_t price{};
price.s = "BTCUSDT";
price.c = "spread";
price.u = 123456789;
price.a = 20000.4;
price.A = 1.25;
price.b = 21000.52;
price.B = 0.58;
price.p = -1;
price.P = -1;
price.st = -1;
price.rt = 1675000000123000;
std::ifstream file_ifstream("../src/avro/fh_price_t.json");
std::stringstream buffer;
buffer << file_ifstream.rdbuf();
std::string schema_json = buffer.str();
Serdes::Conf *sconf = Serdes::Conf::create();
Serdes::Schema *schema;
std::string errstr;
if (sconf->set("schema.registry.url", "http://localhost:8081", errstr))
FATAL("Conf failed: " << errstr);
if (sconf->set("serializer.framing", "cp1", errstr))
FATAL("Conf failed: " << errstr);
Serdes::Avro *serdes = Serdes::Avro::create(sconf, errstr);
if (!serdes)
FATAL("Failed to create Serdes handle: " << errstr);
schema = Serdes::Schema::add(serdes, "fh_price_t", schema_json, errstr);
if (!schema)
FATAL("Failed to register schema " << "fh_price_t" << ": " << errstr);
std::cout << "% Registered schema " << schema->name() << " with id " << schema->id() << std::endl;
avro::GenericDatum *datum = NULL;
std::vector<char> out;
/* Convert JSON to Avro object */
std::string line = to_string_a(price);
json2avro(schema, line, &datum);
//std::cout << to_string_a(price) << std::endl;
/*if (rr == -1) {
FATAL("Failed to convert JSON to Avro " << to_string_a(price) << ": " << errstr);
}
// Serialize Avro
if (serdes->serialize(schema, datum, out, errstr) == -1) {
std::cerr << "% Avro serialization failed: " << errstr << std::endl;
delete datum;
exit(1);
}
delete datum;
std::cout << "Data Size : " << out.size() << std::endl;*/
return 0;
}
When I run it, I get a double free or corruption (out) error.
The error occurs at the output of the function.
I have located the line that causes the error (because when I remove it, the error disappears)
avro::GenericDatum *datum = new avro::GenericDatum(*avro_schema);
I would like to know why and how to solve it.