C inserting string into char pointer

Question

Hi all I trying to assign string into a char * pointer. Below is how I am doing but I am getting this warning: assignment makes integer from pointer without a cast.

What is the correct why to deal with strings in C ?

char* protoName = "";

if(h->extended_hdr.parsed_pkt.l3_proto==0)
    *protoName = "HOPOPT";  
else if(h->extended_hdr.parsed_pkt.l3_proto==1)
    *protoName = "ICMP";    
else if(h->extended_hdr.parsed_pkt.l3_proto==2)
    *protoName = "IGMP";    
else if(h->extended_hdr.parsed_pkt.l3_proto==3)
    *protoName = "IGMP";    
else if(h->extended_hdr.parsed_pkt.l3_proto==4)
    *protoName = "IGMP";

char all[500];

sprintf(all,"IPv4','%s'",* protoName);

Answer 1

If you just want to change which string literal protoName points to, you just need to change

*protoName = "HOPOPT";

to

protoName = "HOPOPT";

*protoName = attempts to write to the first character pointed to by protoName. This won't work in your case as protoName points to a string literal which cannot be modified.

You also need to change your sprintf call to

sprintf(all,"IPv4','%s'", protoName);

The %s format specifier signals that you'll be passing a pointer to a nul-terminated char array. *protoName gives you the character code of the first character pointed to by protoName; sprintf doesn't know this so would treat that character code as the address of the array to read from. You don't own this memory so the effects of reading from it would be undefined; a crash would be likely.

As an aside, if you had a writeable char array and wanted to change its contents, you'd need to use strcpy to copy a new array of chars into it.