filesystems - Attempting to create a FAT file system in C++? -

i'm attempting create fat file system understand basic principle of how supposed set , i'm using struct each fat entry

struct fatentry {     char      name[20];  /* name of file */     uint32_t  pos;       /* position of file on disk (sector, block, else) */     uint32_t  size;      /* size in bytes of file */     uint32_t  mtime;     /* time of last modification */ }; 

i'm creating 2 mb file act file system. there write , read files blocks of 512 bytes each. question how can write struct file? fwrite allow me this? example:

struct fatentry entry1; strcpy(entry1.name, "abc"); entry1.pos = 3; entry1.size = 10; entry1.mtime = 100; cout << entry1.name;  file = fopen("filesys", "w"); fwrite(&entry1,sizeof(entry1),1,file); fclose(file); 

will store struct in bytes? how read this? i'm having trouble understanding when use fread

will store struct in bytes?

• yes. in c++ need explicitly cast &entry1 (void*)

how read this?

• fread((void*)&entry1,sizeof(entry1),1,file);

(but don't forget "r" flag fopen())

the real problem in case struct will padded compiler, efficient access. have use __attribute__((packed)) if using gcc.

[edit] code sample (c, not c++):

struct fatentry entry1 { "abc", 3, 10, 100 }; file* file1 = fopen("filesys", "wb"); fwrite(&entry1, sizeof(struct fatentry), 1, file1); fclose(file1)  struct fatentry entry2 { "", 0, 0, 0 }; file* file2 = fopen("filesys", "rb"); fread(&entry2, sizeof(struct fatentry), 1, file2; fclose(file2) 

you can check read have written earlier:

assert(memcmp(&entry1, &entry2, sizeof(struct fatentry))==0); 

the assert fail if read or write did not succeed (i didn't check this).