help about error: lvalue required left operand assignment c

Hi all,
I am working with complex number and using fftw library ( FFTW Home Page ) to compute fft of some data. But when I am compiling my following simple piece of code , I am getting the above mentioned error.

Code:

---


#define re(c) ((c)[0])                ///< real part of a complex number  as defined by fftw_complex in fftw
#define im(c) ((c)[1])
#include <fftw3.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

unsigned int fs = 16367600;       
double fif = 4.1304E6;
double range = fif;               
double span = 10E3;               
double fd_step = 500;       
double Tint = 1;
 unsigned int l,C1,D1;               
int main()
{
            C1 = ceil((double) fs * 1E-3);
                D1 = ceil(span / fd_step) + 1;
           
            SUM_SS = (fftw_complex *) fftw_malloc(sizeof(fftw_complex) * C1 * D1);
            if (SUM_SS == NULL) {
                fprintf(stderr, "Error allocationg memory fftw operations \n");
               
                }
                for (l = 0; l < C1 *D1; l++) {
                re(SUM_SS[l]) = 0.0;
                im(SUM_SS[l]) = 0.0;
              }
}

---

fftw_malloc behaves like malloc except that it properly aligns the array when SIMD instructions (such as SSE and Altivec) are available. The data is an array of type fftw_complex, which is by default a double[2] composed of the real (in[i][0]) and imaginary (in[i][1]) parts of a complex number.


The error is reported on line re(SUM_SS[l]) = 0.0; and im(SUM_SS[l]) = 0.0; and reported error is
error: lvalue required as left operand of assignment

Please help me

Thanks

How is SUM_SS declared?????

Code:

---

#define re(c) ((c)[0])                ///< real part of a complex number  as defined by fftw_complex in fftw
#define im(c) ((c)[1])

---

Are you sure that it's the correct macro to access real,imag part??

Sorry.... for error in posting the code

Code is :

Code:

---


#define re(c) ((c)[0])                ///< real part of a complex number  as defined by fftw_complex in fftw
#define im(c) ((c)[1])
#include <fftw3.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

unsigned int fs = 16367600;       
double fif = 4.1304E6;
double range = fif;               
double span = 10E3;               
double fd_step = 500;       
double Tint = 1;
 unsigned int l,C1,D1;       
fftw_complex *SUM_SS;
       
int main()
{
            C1 = ceil((double) fs * 1E-3);
                D1 = ceil(span / fd_step) + 1;
           
            SUM_SS = (fftw_complex *) fftw_malloc(sizeof(fftw_complex) * C1 * D1);
            if (SUM_SS == NULL) {
                fprintf(stderr, "Error allocationg memory fftw operations \n");
               
                }
                for (l = 0; l < C1 *D1; l++) {
                re(SUM_SS[l]) = 0.0;
                im(SUM_SS[l]) = 0.0;
              }
}

---

What seems to be the error is that fftw_complex is a structure and you have a pointer to it. Hence, SUM_SS[l] is a fftw_complex, thus the macro expands to:
SUM_SS[1][0] which won't work since fftw_complex is not an array. This is what I can guess from the code you have posted.
Also, make sure to move all your global vars into main. And the variables you don't intend to change should be const.