Build errors

[dellthinker]

Hello. I'm trying to build a packet sniffer from here. I got about 5 errors when trying to build this source code.

'local->h_addr_list[in]' could be '0':  this does not adhere to the specification for the function 'memcpy'. 
'temp_data' could be '0':  this does not adhere to the specification for the function 'fwrite'. 
Return value ignored: '_getch'.
Dereferencing NULL pointer 'buf'. 
Using uninitialized memory 'addr'.
'localtime': This function or variable may be unsafe. Consider using localtime_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
'inet_ntoa': Use inet_ntop() or InetNtop() instead or define _WINSOCK_DEPRECATED_NO_WARNINGS to disable deprecated API warnings
'inet_ntoa': Use inet_ntop() or InetNtop() instead or define _WINSOCK_DEPRECATED_NO_WARNINGS to disable deprecated API warnings
'gethostbyname': Use getaddrinfo() or GetAddrInfoW() instead or define _WINSOCK_DEPRECATED_NO_WARNINGS to disable deprecated API warnings

[salem_c]

Well that's what you get when you compile decade++ old code with new tools able to inspect the code for more issues.

> 'local->h_addr_list[in]' could be '0':

    for (i = 0; local->h_addr_list[i] != 0; i++) {
        memcpy(&addr, local->h_addr_list[i], sizeof(struct in_addr));
        printf("Interface Number: %d Address: %s\n", i, inet_ntoa(addr));
    }
    printf("\nEnter the interface number you would like to sniff: ");
    scanf_s("%d", &in);
    memset(&dest, 0, sizeof(dest));
    memcpy(&dest.sin_addr.s_addr, local->h_addr_list[in], sizeof(dest.sin_addr.s_addr));

The compiler learnt from the for loop that some subscript of h_addr_list yields a NULL pointer.
Further, neither the result of scanf_s is checked, nor the resulting value stored in in.

    int numValidInterfaces = 0;
    for (i = 0; local->h_addr_list[i] != 0; i++) {
        memcpy(&addr, local->h_addr_list[i], sizeof(struct in_addr));
        printf("Interface Number: %d Address: %s\n", i, inet_ntoa(addr));
        numValidInterfaces++;
    }
    printf("\nEnter the interface number you would like to sniff: ");
    // 
    if ( scanf_s("%d", &in) == 1 && in >= 0 && in < numValidInterfaces ) {
        memset(&dest, 0, sizeof(dest));
        memcpy(&dest.sin_addr.s_addr, local->h_addr_list[in], sizeof(dest.sin_addr.s_addr));
    } else {
        // Some error message about the user not being able to
        // follow instructions.
        // Then return with an error.
    }

> 'temp_data' could be '0':
You don't check for the malloc call returning NULL.

    char *temp_data = (char *)malloc(DATA_SIZE);

[dellthinker]

Well that's what you get when you compile decade++ old code with new tools able to inspect the code for more issues.

I was looking for a packet sniffer to learn from and found the first I could find. I suppose I'll look a little deeper this time.

[2kaud]

There are loads of older c/c++ code available on the Internet. You may find similar issues with other found code.

You don't say which compiler/os you're using. Note that some code is for a Posix system (eg Linux/gcc) and isn't easily converted to say Windows/Visual Studio as there are header differences.

[dellthinker]

There are loads of older c/c++ code available on the Internet. You may find similar issues with other found code.

I find that looking for code that old is ridiculously difficult building when you can't reach the authors. Been searching all through github for working src.

You don't say which compiler/os you're using. Note that some code is for a Posix system (eg Linux/gcc) and isn't easily converted to say Windows/Visual Studio as there are header differences.

Visual C++ 2022.

Starting from scratch again....