CODEWITHSUNDEEP
c++cpointersvariable-assignment
SDG
SDG

Reputation: 2342

error assignment to expression with array type

I have a function named unpack, and compiling the C++ code leads to a couple of errors. The code is below: 

static void unpack(void *v, ekf_t *ekf, int n, int m) {
    /* skip over n, m in data structure */
    char *cptr = (char *) v;
    cptr += 2 * sizeof(int);

    double *dptr = (double *) cptr;
    ekf->x = dptr;
    dptr += n;
    ekf->P = dptr;
    dptr += n * n;
    ekf->Q = dptr;
    dptr += n * n;
    ekf->R = dptr;
    dptr += m * m;
    ekf->G = dptr;
    dptr += n * m;
    ekf->F = dptr;
    dptr += n * n;
    ekf->H = dptr;
    dptr += m * n;
    ekf->Ht = dptr;
    dptr += n * m;
    ekf->Ft = dptr;
    dptr += n * n;
    ekf->Pp = dptr;
    dptr += n * n;
    ekf->fx = dptr;
    dptr += n;
    ekf->hx = dptr;
    dptr += m;
    ekf->tmp0 = dptr;
    dptr += n * n;
    ekf->tmp1 = dptr;
    dptr += n * m;
    ekf->tmp2 = dptr;
    dptr += m * n;
    ekf->tmp3 = dptr;
    dptr += m * m;
    ekf->tmp4 = dptr;
    dptr += m * m;
    ekf->tmp5 = dptr;
}

And I get these errors propagated over every line of the code: 

.../src/ekf.c:203:12: error: assignment to expression with array type
     ekf->x = dptr;
            ^
.../src/ekf.c:205:12: error: assignment to expression with array type
     ekf->P = dptr;

It should be noted that the code unpack was grabbed from a C library. I have tried using an extern, but this does not seem to work too well. Now, when I make the original repository (https://github.com/simondlevy/TinyEKF), it seems to compile without a problem. The compile command for TinyEKF, which contains and uses this code, is:

gcc -Wall -I. -I../../src -o gps_ekf gps_ekf.c ../../src/tiny_ekf.c -lm

This is found within /extras/c/ within the repository and certainly uses the unpack function.

Upvotes: 0

Views: 145

Answers (1)

Blaze
Blaze

Reputation: 16876

According to this, ekf.x is of type double x[]. You can't just assign to an array like ekf->x = dptr;, as the error says. If you want to copy data from dptr to ekf->x, you can use memcpy:

memcpy(&ekf->x, dptr, sizeof(ekf->x));

The same goes for all the other assignments, most of those fields are double arrays.

Upvotes: 1

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