Program crash after trying to access and write to structure member

问题

Working in Visual Studio in C and trying to do fft of some samples. When I attempt writing some value to member of struct my program crash and I get error access violation writing location 0x00000000.

First, I tried to use this C code, but got errors:

kiss_fft_cpx *cx_in = new kiss_fft_cpx[nfft];  
kiss_fft_cpx *cx_out = new kiss_fft_cpx[nfft];

in this two lines. Okay there is no new in C. I tried to modify it but I can not do it. I tried

kiss_fft_cpx *cx_in[1024];
kiss_fft_cpx *cx_out[1024];

and few lines after i tried to pass some value with

cx_in[brojac]->r = i; // this is where program breaks
cx_in[brojac]->i = q;

from kiss_fft.h header file

typedef struct {
   kiss_fft_scalar r;
   kiss_fft_scalar i;
} kiss_fft_cpx;

typedef struct kiss_fft_state* kiss_f;

//beginning of main 
kiss_fft_cpx *cx_in[1024];
kiss_fft_cpx *cx_out[1024];

//after doing some sampling 
cx_in[brojac]->r = i; // this is where program crash
cx_in[brojac]->i = q;

回答1:

cx_in and cx_out are just pointers to an array of structs. You need to allocate the memory.

kiss_fft_cpx *cx_in = malloc(1024*sizeof(kiss_fft_cpx));
kiss_fft_cpx *cx_out = malloc(1024*sizeof(kiss_fft_cpx));

回答2:

kiss_fft_cpx *cx_in = new kiss_fft_cpx[nfft];

In C++ this will allocate an array of structs. The analogous part in C is

struct kiss_fft_cpx *cx_in = malloc(nfft * sizeof(struct kiss_fft_cpx));

You can use this as

cx_in[brojac].r = i;  // where 0 <= brojac < nfft

来源：https://stackoverflow.com/questions/57708683/program-crash-after-trying-to-access-and-write-to-structure-member

标签

visual-studio

struct

fft