获取指针指向的数组的单个元素的 sizeof — char 指针

Question

I have a char *c="hello" but if I do sizeof(*c) it will return 1 (1 byte). I like to know what is this size. Is it size of individual character of first memory address for char *c="hello" like sizeof('h') and when I do sizeof(*(c+1)) etc still returns 1.

this is my system details

Architecture: x86_64

CPU op-mode(s): 32-bit, 64-bit

Address sizes: 36 bits physical, 48 bits virtual

CPU(s): 4

also In bigger project I assigned char *c=payload_body_text the function is like following in the same project

 somefunction(struct tpacket3_hdr *ppd)
  {
    struct ethhdr *eth = (struct ethhdr *) (ppd + ppd->tp_mac);
    struct iphdr *ip = (struct iphdr *) ( eth + ETH_HLEN);
    struct tcphdr *tcp=(struct tcphdr *)(ip+sizeof(struct iphdr));
    char *payload_body=(char *)(tcp + tcp->doff) ;
 }

So basically I like to know is payload_body is pointing to some area of object which is pointed to by ppd ? which I am sure my OS has allocated before packet entered into tcp-ip stack of the kernel. tpacket3_hdr is from Packet MMAP. in a way you can call it like a packet.

Answer 1

Size() operator gives you the size of whole character. It gives you the size required to assign the variable in memory. In case of 64 bit or 34 bit system, character variable reserve 1 byte address in memory.

sizeof(*c+1) will return 4 (in case of 64 bit; in case of 32 bit it is 2) not 1. Check it again.

Because sizeof character and integer is 1 and 4 respectively. Result of character + integer expression is a integer. So, *c+1 will generate an integer variable and hence it will print 4 because sizeof integer variable is 4