Dynamically allocating an array of a struct

Question

I am having a hard time dealing with malloc in C especially when allocating for array of struct. I have a program that basically store all the filenames and filesize in an array of struct. I got my program working without using malloc but I dont really like this way of programming. Could I get any help using malloc, in my program?

int getNumberOfFiles(char *path)
{
 int totalfiles = 0;
 DIR *d;
 struct dirent *dir;
 struct stat cstat;
 d = opendir(path);
 while(( dir = readdir(d)) != NULL) {
     totalfiles++;
}
return totalfiles;
}

int main()
{

      int totalfiles = getNumberOfFiles(".");
      int i =0;
      DIR *d;
      struct dirent *dir; 
      d = opendir(".");
      struct fileStruct fileobjarray[totalfiles];
      struct stat mystat;

       while(( dir = readdir(d)) != NULL) {
        fileobjarray[i].filesize=mystat.st_size;
        strcpy (fileobjarray[i].filename ,dir->d_name );
        i++;
      }

}

As you can see, I made a function called getnumberoffiles() to get the size to allocate statically.

Answer 1

struct fileStruct fileobjarray[totalfiles];

fileobjarray is a VLA array of size totalfiles of fileStruct structure. To allocate using malloc we can write:

struct fileStruct *fileobjarray = malloc(totalfiles * sizeof(*fileobjarray));

We would allocate memory for an array of totalfiles elements, with each element of sizeof(*fileobjarray) = sizeof(struct fileStruct) size. Sometimes calloc is more preferable call in C, as it protects (on some platforms) against overflow:

struct fileStruct *fileobjarray = calloc(totalfiles, sizeof(*fileobjarray));

And remember to free() .

int getNumberOfFiles(char *path)
{
 int totalfiles = 0;
 DIR *d;
 struct dirent *dir;
 struct stat cstat;
 d = opendir(path);
 while(( dir = readdir(d)) != NULL) {
     totalfiles++;
}
return totalfiles;
}

int main()
{

      int totalfiles = getNumberOfFiles(".");
      int i =0;
      DIR *d;
      struct dirent *dir; 
      d = opendir(".");
      struct fileStruct *fileobjarray = calloc(totalfiles, sizeof(*fileobjarray));
      if (fileobjarray == NULL) {
            fprintf(stderr, "Error allocating memory!\n");
            return -1;
      }
      struct stat mystat;

      while(( dir = readdir(d)) != NULL) {
        fileobjarray[i].filesize=mystat.st_size;
        strcpy (fileobjarray[i].filename ,dir->d_name );
        i++;
      }
      free(fileobjarray);
}