CODEWITHSUNDEEP
c++charintbyte
Alejoo
Alejoo

Reputation: 13

Int append to char, does not behave as I expect

I have this issue with assign an int to a char. I have a const char * data, that works like a storage of sizes of differents objects. I use this, to verify if the data have the same size that a object, if is thus, then I append a 2 integer to data. The problem is, that I expected that when I append 2 to data, move 2 positions in ASCII table, but how data behaves as a string, I cannot understand how works this addition.

Example: I have a const char* data that store a char '`', and that have a value of 96, if I make :

data += 2;

I would expect the result to be b, but is < with a value 60.

I use a function sys_log to show what happen.

function Boot:

     void Boot(const char* data){
     [...]
     /*
     * OBJECT PROTO
     */

    sys_log(0, "BOOT: OBJ PROTO data string: data = %s", data);
    sys_log(0, "BOOT: OBJ PROTO size of data: %d", decode_2bytes(data));

    if (decode_2bytes(data) != sizeof(TObjectProto))
    {
        sys_err("object proto table size error");
        thecore_shutdown();
        return;
    }
    sys_log(0, "BOOT: OBJ PROTO data after decode_2bytes(data): data = %s", data);
    data += 2;
    sys_log(0, "BOOT: OBJ PROTO data str + 2: data = %s", data);

    size = decode_2bytes(data);
    sys_log(0, "BOOT: OBJ PROTO data to size: size = %d", size);

    data += 2;
    sys_log(0, "BOOT: OBJ PROTO data str + 2: data = %s", data);
    sys_log(0, "BOOT: OBJ PROTO data to size: size = %d", decode_2bytes(data));

    CManager::instance().LoadObjectProto((TObjectProto *) data, size);

    sys_log(0, "To data  assign %d * %d", size, sizeof(TObject));
    data += size * sizeof(TObjectProto);
    sys_log(0, "BOOT: OBJ PROTO  data str: data = %s",  data);

    [...]

decode_2bytes():

inline WORD decode_2bytes(const BYTE *a)
{
    return (*((WORD *) a));
}

sys_log :

Apr 12 09:05:54.205886 :: BOOT: OBJ PROTO data string: data = `
Apr 12 09:05:54.205914 :: BOOT: OBJ PROTO size of data: 96
Apr 12 09:05:54.205924 :: BOOT: OBJ PROTO data after decode_2bytes(data): data = `
Apr 12 09:05:54.205933 :: BOOT: OBJ PROTO data str + 2: data = <
Apr 12 09:05:54.205948 :: BOOT: OBJ PROTO data to size: size = 60
Apr 12 09:05:54.205961 :: BOOT: OBJ PROTO data str + 2: data = ½6
Apr 12 09:05:54.205970 :: BOOT: OBJ PROTO data to size: size = 14013
Apr 12 09:05:54.209238 :: To data  assign 60 * 40
Apr 12 09:05:54.209247 :: BOOT: OBJ PROTO  data str: data = (

As can see in sys_log, I show what contain data, the value, and the result that I obtain when add 2.

Upvotes: 1

Views: 73

Answers (1)

zett42
zett42

Reputation: 27776

data += 2;

I would expect the result to be b, but is < with a value 60.

You just increment the pointer by 2, so it will point to the 3rd character of the string, which is <. It may even be some random value if the strings happens to end before that.

To increment the value that the pointer points to, you have to dereference the pointer:

*data += 2;

But this will trigger a compiler error, because data is declared as const char*.

If you want to modify the string, change the parameter to char* data.

Upvotes: 2

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