c - fread into array of structs segmentation fault -

i've been working on code awhile , i've run seg fault can't seem debug. here's relevant code:

typedef struct halo* halo;   struct halo   {       float x, y, z;       float vx, vy, vz;       int n200a;       float m200a;       float r200a;       int n200c;       float m200c;       float r200c;       int n500a;       float m500a;       float r500a;       int n500c;       float m500c;       float r500c;   };   

global variable:

halo *halo_catalog;

the function fails:

int loadhalocatalog(char *filename)   {       file *catalog_file;       long long halo_num;      catalog_file = fopen(filename, "rb");     if (catalog_file == null) {         printf("could not open halo catalog: %s\n", filename);         return -1;     }     if (fread(&halo_num, sizeof(long long), 1, catalog_file) < 0) {           printf("could not read number of halos\n");           return -1;       }       halo_catalog = (halo *)calloc(halo_num, sizeof(struct halo));       if (fread(halo_catalog, sizeof(struct halo), halo_num, catalog_file) < 0) {           printf("could not read number of halos\n");           return -1;       }       printf("%f\n", halo_catalog[10000]->x);       printf("done\n");       fclose(catalog_file);       return (int)halo_num;   } 

it fails on "printf("%f\n", halo_catalog[10000]->x);" line, or other access memory allocated after fread call. know passing in valid file, can read halo_num correctly. collects correct halo objects fread call, when call fread , check return returns halo_num.

thanks!

typedef struct halo* halo; 

that's terrible idea, , cause of problems.

you have global variable

halo *halo_catalog; 

so struct halo**. in

halo_catalog = (halo *)calloc(halo_num, sizeof(struct halo));   if (fread(halo_catalog, sizeof(struct halo), halo_num, catalog_file) < 0) { 

you use if struct halo*.

then index

printf("%f\n", halo_catalog[10000]->x); 

at distance of 10000 * sizeof(struct halo*) bytes halo_catalog points, , interpret bytes @ location - part of values of floats or ints read in, not pointers - , try access x component of whatever arbitrary location result of misinterpretation.

you should

typedef struct halo halo; 

and use halo_catalog[10000].x fix issue.

another issue fread returns number of items has read, if smaller requested number, can still positive number.

capture return value of fread, , use determine whether reading successful. also, sure 10000 valid index before trying print halo_catalog[10000].x.