Dlang字符串转换为char *转换

Question

I've got this code reading from a bin file. the data is held in an array of structs and null terminated My goal is to read data, written in c-code with write (filehandle, (char *)arrayOfCELLs, sizeof(arrayOfCELLs); to a file, into the same structure arrayOfCELLs using D.

My problem is that in c I read the file into a struct arr[] via a cast to (char *)

read(filehandle, (char *)arrayOfStructs, sizeof(arrayOfStructs)

In DI found out through rcorre that led me to rawRead

auto buffer = FileHandle.rawRead(arrayOfStructs)

where the buffer gets the data to the sizeof arrayOfStructs.

However, here comes my problem, the buffer seems to get the rawdata including nulltermination but all positioned in [0] of the receiving Array, also, I don't understand/know what the datatype it is(CELL[] or string[] or .....

struct CELL{ char [20] name, int sect, int type ...};
struct CELL [50] arrayOfCELLs;
auto buffer = ..rawRead(arrayOfCELLs)

received data in the buffer is (part of it) this

[CELL("TEST\0feed\0\0\0\0\0\0\0\0\0\0\0", 1, 1,

The first is the name, "TEST" followed by null-termination, then sect = 1, ptyp = 1 . Now the second CELL holds this

CELL("\x01\0\0\0\x02\0\0\0N\0\0\0\x04\0\0\0\x02\0\0\0", 65656, 655375,

And that is all wrong, Should be "test" and 2,1, If I do a cat in the terminal I get

anders$ cat cellspec
TESTfeedOx
atestTailingNx
aOF2 cycl primO?

Question, any ideas why this is and what can I do to get it right?

Answer 1

What you probably need are calls to toStringz() and fromStringz(). (Documentation page: http://dlang.org/phobos/std_string.html )

Example (from the abovementioned page):

import core.stdc.string : strlen;
import std.conv : to;

auto p = toStringz("foo");
assert(strlen(p) == 3);
const(char)[] foo = "abbzxyzzy";
p = toStringz(foo[3..5]);
assert(strlen(p) == 2);

assert(fromStringz(null) == null);
assert(fromStringz("foo") == "foo");

Also, rawRead() returns the same type as the type of the buffer. So, since you have

auto buffer = f.rawRead(cellTab);

, then the buffer is already an array of CELL's... You should be able to use it with, say buffer[0].name to grab the name of the first cell...

Keep in mind that .name is actually char[20]. You really want to convert it to a string if you want to do some operations with it.

Answer 2

I have found out what the problem is with the conversions. The long and unsigned long in C is not the same size in Dlang long and ulong

Solution/conclusion is when coding in D-lang and using C typed data in files, in order to get the reading correct one needs to beware that D-lang type size might not be equal to C size. In my case the code changed to use c_long and c_ulong to get the reading correct. After that all was well reading data. Happy days