Erlang Driver Errors-CodePudding

I have to write an Erlang driver so I started by triying a little one : driverc.c , the code is simple, the Driver Erlang Data is the address of a long number and each call to the driver is to increment this number by n or multipliying this number by n, n is just one digit number (0,...., 9) and is passed as char , the code is:

#include<stdio.h>
#include<stdlib.h>
#include<erl_driver.h>
#include<ei.h>
#include<string.h>

#define SOMME 1
#define PRODUIT 2

static ErlDrvData start(ErlDrvPort port, char *command) ;

static void stop(ErlDrvData data) ;

static ErlDrvSSizeT control(ErlDrvData data, unsigned int command, char *buf, ErlDrvSizeT len, char **rbuf, ErlDrvSizeT rlen);

static long *number;

static ErlDrvEntry myentry={
NULL,
start,
stop,
NULL,
NULL,
NULL,
"driverc",
NULL,
NULL,
control,
NULL,
NULL,
NULL,
NULL,
NULL
};

DRIVER_INIT(driverc)
{return &myentry;}

ErlDrvData start(ErlDrvPort port, char *command)
{number=(long*)driver_alloc(sizeof(long)) ;
*number=0;
set_port_control_flags(port,PORT_CONTROL_FLAG_BINARY);
return (ErlDrvData)number;
}

void stop(ErlDrvData data)
{long *olddata;
 olddata=(long*)data;
 driver_free(olddata);
}

ErlDrvSSizeT control(ErlDrvData data, insigned int command, char *buf, ErlDrvSizeT len, char **buf, ErlDrvSizeT rlen)
{long    reply, m, *olddata, newdata;
 int     index, result, n;
 char    c;

 c=*buf;
 n=c-'0'; /* convert character representation to true integer digit */
 m=(long)n;
 olddata=(long*)data;
 index=0;
 switch (command) {
 case SOMME : newdata=(*olddata) m;
              *olddata=newdata;
              reply=newdata;
              break;

 case PRODUIT : newdata=(*olddata)*m;
                *olddata=newdata;
                reply=newdata;
                break;

 default : reply=-1;
                 break;
                   }
result=ei_encode_long(*rbuf,&index,reply) ; /* this function convert a long number (reply) to binary and write it in *rbuf */
return sizeof(reply) ;
}

When I tried to compile it, it returns errors that I can't know where is the problem, the shell output is below.

cc driverc.c  -I/usr/local/lib/erlang/usr/include

error : undefined symbol : main
referenced by .... 
error : undefined symbol : driver_alloc
referenced by .... 
error : undefined symbol : set_port_control_flags
referenced by .... 
error : undefined symbol : ei_encode_long
referenced by .... 
error : linked command failed with exit code 1 ....

https://ibb.co/LnTDtmt

CodePudding user response：

From the documentation on "Compiling and Linking the Sample Driver":

The driver is to be compiled and linked to a shared library (DLL on Windows). With gcc, this is done with link flags -shared and -fpic. As we use the ei library, we should include it too.

The linker complains about not finding main, because it thinks it's building a stand-alone program. Building it as a shared library should fix that.

There is a sample Makefile in the Erlang/OTP repository that might be useful - it includes all the required flags.