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c++gccsmbus

SMBUS undefined reference

I'm trying to make simple program in c++ to read from SMBus, but can't even build program sample. I'm building with gcc(9.4.0) on Ubuntu 20.04.5 LTS.

I've installed

  • libi2c-dev
  • i2c-tools

Code:

#include <cstdio>

extern "C" {
    #include <linux/i2c.h>
    #include <linux/i2c-dev.h>
    #include <i2c/smbus.h>
}
#include <fcntl.h> 
#include <sys/ioctl.h> 

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

    int file;
    int adapter_nr = 6;
    char filename[20];
    snprintf(filename, 19, "/dev/i2c-%d", adapter_nr);
    file = open(filename, O_RDWR);
    if (file < 0) {
        return(1);
    }

    int addr = 0x0b;
    if (ioctl(file, I2C_SLAVE, addr) < 0) {
        return(1);
        return(1);
    }

    __u8 reg = 0x0d;
    __s32 res;
    char buf[10];

    res = i2c_smbus_read_word_data(file, reg);

    return 0;

}

Build command: gcc -li2c test_inc.cpp

but I'm getting following error:

test_inc.cpp:(.text+0xb9): undefined reference to `i2c_smbus_read_word_data'
collect2: error: ld returned 1 exit status

Linking i2c is passed as argument, and shared object exists libi2c

Can anyone help me to solve this riddle ?

I tried to update apts and reinstalled all packages I also added "-I path_to_so_file" to gcc

Solution

  • The order of the source file and the library is relevant. The following command should work:

    gcc test_inc.cpp -li2c