Calling C/C++ Code in Codon

First, use the following command to install eoscdt for compiling C or C++ code:

python3 -m pip install -U eoscdt

Next, let's compile the say_hello function as an example to demonstrate how to compile code:

If the source file is in C, for example:

say_hello.c

void prints(const char *s);

void say_hello(const char *s) {
    prints(s);
}

Then use the following command to compile:

cdt-cc -c -o say_hello.o say_hello.c

If the source file is C++ code, for example:

say_hello.cpp

extern "C" void prints(const char *s);

extern "C" void say_hello(const char *s) {
    prints(s);
}

Then use the following command to compile:

cdt-cpp -c -o say_hello.o say_hello.cpp

Note that if it is a C++ file, you need to add extern "C" before the function, otherwise a link error will occur.

Next, let's see how to use the say_hello function in Codon:

test.codon

from chain.contract import Contract

from C import say_hello(cobj);

@contract(main=True)
class MyContract(Contract):

    @action("sayhello")
    def say_hello(self):
        say_hello("hello, world".c_str())

Here,

from C import say_hello(cobj);

tells the Codon compiler to link the say_hello C function. All pointer types in C/C++ correspond to the cobj type in Codon.

The following line of code calls the C function, the value returned by c_str is of cobj type, equivalent to const char * type in C/C++.

say_hello("abc".c_str())

Next, use the following command to compile:

python-contract build --linker-flags="say_hello.o" test.codon

Here, --linker-flags="say_hello.o" tells the compiler to link the say_hello.o obj file.

Next, use the following code to test:

test.py:

import os
from ipyeos import eos
from ipyeos import chaintester
from ipyeos.chaintester import ChainTester
from ipyeos import log
from pyeoskit import eosapi

chaintester.chain_config['contracts_console'] = True
eos.set_log_level("default", 3)

logger = log.get_logger(__name__)

dir_name = os.path.dirname(os.path.abspath(__file__))

def init_test(contract_name):
    t = ChainTester(True)
    wasm_file = os.path.join(dir_name, f'{contract_name}.wasm')
    with open(wasm_file, 'rb') as f:
        code = f.read()

    abi_file = os.path.join(dir_name, f'{contract_name}.abi')
    with open(abi_file, 'r') as f:
        abi = f.read()

    t.deploy_contract('hello', code, abi)
    t.produce_block()
    eos.set_log_level("default", 1)
    return t

def test_say_hello():
    t = init_test('test')
    ret = t.push_action('hello', 'sayhello', "", {'hello': 'active'})
    t.produce_block()
    logger.info("++++++++++%s\n", ret['elapsed'])

Run the test:

ipyeos -m pytest -s -x test.py -k test_say_hello

You should see the following output:

hello, world

Full Source Code

Calling C/C++ Code in Codon

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