CODEWITHSUNDEEP
carrays
Anthony
Anthony

Reputation: 325

How to initialize char[] from a define

I want to copy my define into my var IP:

#define IP_ADDR {169, 254, 0, 3}

struct
{
  // ....
  char IP[4];

} COM_INFO;

memcpy(COM_INFO.IP, IP_ADDR, 4);

But it doesn't work.

Upvotes: 2

Views: 164

Answers (2)

Fiddling Bits
Fiddling Bits

Reputation: 8861

Your define must be like this:

#define IP_ADDR ((unsigned char []){169, 254, 0, 3})

Now you can use memcpy on it.

Example Code

#include <stdio.h>
#include <string.h>

#define IP_ADDR ((unsigned char []){169, 254, 0, 3})

int main(void)
{
    unsigned char ip[4];

    memcpy(ip, IP_ADDR, 4);

    printf("%u.%u.%u.%u\n", ip[0], ip[1], ip[2], ip[3]);

    return 0;
}

Example Output

169.254.0.3

Upvotes: 2

bblincoe
bblincoe

Reputation: 2483

IP_ADDR will be pasted wherever its referenced (by the pre-processor). So, you could do something like the following:

int main(int argc, const char* argv[])
{
    // Initialize the COM_INFO structure.
    COM_INFO comInfo = { 
        // ...
        IP_ADDR,  // {169, 254, 0, 3} will be pasted here
        // ...
    };

    return 0;
}

Upvotes: 1

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