Trouble translating to C API

[Alex Shroyer]

Hi, I can build and run a C++ example and get the expected output. However when I try to translate this to use the C API, I get an error.

This C++ code works:

$ cat main.c

#include<arrayfire.h>

int main(void) {

    af::array M1 = af::randu(2,4);

    af::array M2 = af::randu(4,1);

    af::array result = af::matmul(M1, M2);

    af_print(result);

}

$ g++ -std=c++11 main.cpp -I/opt/arrayfire/include -lafcpu -L/opt/arrayfire/lib64

$ ./a.out

result

[2 1 1 1]

    0.9704

    0.3218

I attempted to translate this into a C API version. It compiles, but the print function produces "208" error (AF_ERR_DEVICE). What causes this error and how can I fix it?

Below is the C version, compile command, and output:

$ cat main.c

#include<arrayfire.h>

#include<stdio.h>

int main() {

    af_array M1, M2, result;

    dim_t d1[] = {2, 4};

    dim_t d2[] = {4, 1};

    if (AF_SUCCESS != af_randu(&M1, 2, d1, f64)) return 1;

    if (AF_SUCCESS != af_randu(&M2, 2, d2, f64)) return 1;

    if (AF_SUCCESS != af_matmul(&result, M1, M2, AF_MAT_NONE, AF_MAT_NONE)) return 1;

    printf("before\n");

    printf("%d\n", af_print_array(&result));

    printf("after\n");

    return 0;

}

$ gcc -std=c11 main.c -I/opt/arrayfire/include -lafcpu -L/opt/arrayfire/lib64

$ ./a.out

before

208

after

Thanks in advance!

[Alex Shroyer]

Silly mistake, I should not have used &result, just result. Works now!

[Alex Shroyer]

A follow-up question: what is the rationale behind some array parameters being passed by pointer and others being passed by value?

[uma...@gmail.com]

Typically, the af_array objects that are assigned will be passed as a pointer and the others are passed as value because they are input and will not be changed in the operation. The af_array is just a handle to an internal data structure that represents the af_array object. Its like passing in a void*.

Umar

[Alex Shroyer]

Thanks Umar, that makes sense.