file.write(buf, len)

Other Hardware Storage
1

in my progect i use a user defined type

typedef struct {
  char    barcode [14];
  char    nam [21];
  char    dfName   [ 9];
  int     unit    ;
  float   price ;
  long    quant      ;
  char    DatStr      [ 6];
  long    Id  ;
  long    found  ;
} Itemrec;
Itemrec thisItem ;

when i try to write it to the file i read from using this command

 myFile.write(    &thisItem     );

it changes the length of file and thus destroying the sequence
when i try to use

myFile.write(    &thisItem,  sizeof(thisItem)   );

it gives me error >>>
SD_Card:79: error: no matching function for call to 'SDLib::File::write(Itemrec*, unsigned int)
i would appreciate if some one give me the right syntax
thank you

2

Why are you trying to write the address of the struct to the file? That's what the & operator gives you.

Just use:

myFile.write((byte *)thisIten, sizeof(Itemrec));

The cast is necessary because thisItem is not a byte array, but it can be treated like one, so we lie to the compiler, and tell it that thisItem IS a byte array.

3

thank you Paul for your help i tried the syntax you suggested but my compiler discovered i am lying and said "SD_Card:136: error: invalid cast from type 'Itemrec' to type 'byte* {aka unsigned char*}'"
i come from vb background so i am not well used to casting rules
i hope for more help
thanks again
fidamon

4

i found a solution for the cast problem on c++ - Convert struct into bytes - Stack Overflow

   char* itemBytes = reinterpret_cast<char*>(&thisItem);

  myFile.write(  itemBytes, sizeof(Itemrec));

i will try it and see
thank you PaulS for your help
Fidamon

5

it worked