inet_ntoa problem

[ramg75]

inet_ntoa () library call is often used to print the IP address in a dotted decimal format. Care should be taken while using two or more inet_ntoa () library calls in a single statement for example

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#include <stdio.h>
#include <netinet/in.h>
#include <sys/socket.h>

struct inaddr ipaddr;
struct inaddr maskaddr;

ipaddr.s_addr = 0x01020304;
maskaddr.s_addr = 0xffffffff;

sprintf (buff, `IP Addr %s\t Mask %s\n`,
inet_ntoa (ipaddr),
inet_ntoa (maskaddr));

When we print the content of the `buff` we will be surprised to see the `ipaddr` is repeated two times (`IP Addr 1.2.3.4 Mask 1.2.3.4`). This is because the inet_ntoa () returns the pointer to a string. Successive calls OVERWRITES the existing memory. To avoid this inet_ntoa () call should be used one by one and not in the same line. Correct usage is
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sprintf (buff, `%s`, inet_ntoa (ipaddr));
sprintf (buff+4, `%s`, inet_ntoa (maskaddr));