Question

I am working on a project where I need to read data from a binary file. I am trying to store the data into a char buffer. Suppose the binary file consisted of a character, an int and a double what size would the char buffer need to be ? And how would I convert back into int’s and doubles ?

I am reading the data into a char buffer because it would improve the speed of my program.

Thanks!

Answer 1

The following example program fread()s the first DATASIZE sets of a char, an int and a float from a file specified on the command line:

typedef struct Data_s {
  char c;
  int i;
  float f;
} Data_t;

#define DATASIZE 3

int main(int argc, char ** argv) {
  if (1 >= argc) {
    fprintf(stderr, "usage: %s <file name>\n", argv[0]);
    return EXIT_SUCCESS;
  }

  {
    FILE * f = fopen(argv[1], "r");
    if (!f) {
      perror("fopen() failed.");
      return EXIT_FAILURE;
    }

    {
      Data_t data[DATASIZE];
      size_t sizeData = sizeof(*data);
      size_t sizeToRead = sizeof(data)/sizeData;
      memset(data, 0, sizeToRead * sizeData);
      size_t sizeRead = fread(&data, sizeData, sizeToRead, f);
      if (0 != fclose(f))
        perror("fclose() failed,");
      if (sizeToRead != sizeRead) {
        perror("fread() failed.");
        return EXIT_FAILURE;
      }

      for (size_t i = 0; i < sizeToRead; ++ i)
        printf("read c=0x%02hhx, i=%d, f=%f from '%s'\n", data[i].c, data[i].i, data[i].f, argv[1]);
    }
  }

  return EXIT_SUCCESS;
}