compiling npcap tutorial code

[dellthinker]

I can't seem to get this code snippet to compile..

int main()
{
    pcap_if_t* alldevs;
    pcap_if_t* d;
    int i = 0;
    char errbuf[PCAP_ERRBUF_SIZE];

    /* Retrieve the device list from the local machine */
    if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING,
        NULL /* auth is not needed */,
        &alldevs, errbuf) == -1)
    {
        fprintf(stderr,
            "Error in pcap_findalldevs_ex: %s\n",
            errbuf);
        exit(1);
    }

    /* Print the list */
    for (d = alldevs; d != NULL; d = d->next)
    {
        printf("%d. %s", ++i, d->name);
        if (d->description)
            printf(" (%s)\n", d->description);
        else
            printf(" (No description available)\n");
    }

    if (i == 0)
    {
        printf("\nNo interfaces found! Make sure Npcap is installed.\n");
        return;
    }

    /* We don't need any more the device list. Free it */
    pcap_freealldevs(alldevs);
 }

I got the error: 'main': function must return a value on line 69. I added the library to the project I don't know what to do now about the error.

[salem_c]

> I got the error: 'main': function must return a value on line 69.

So just add this to the end of main
return 0;

[dellthinker]

> I got the error: 'main': function must return a value on line 69.

So just add this to the end of main
return 0;

That threw a lot of errors.

Severity	Code	Description	Project	File	Line	Suppression State	Details
Error	LNK1120	2 unresolved externals	Project2	C:\Users\rooth\source\repos\Project2\x64\Debug\Project2.exe	1		
Severity	Code	Description	Project	File	Line	Suppression State	Details
Error	LNK2019	unresolved external symbol pcap_freealldevs referenced in function main	Project2	C:\Users\rooth\source\repos\Project2\Project2\Source.obj	1		
Severity	Code	Description	Project	File	Line	Suppression State	Details
Error	LNK2019	unresolved external symbol pcap_findalldevs_ex referenced in function main	Project2	C:\Users\rooth\source\repos\Project2\Project2\Source.obj	1		

Severity	Code	Description	Project	File	Line	Suppression State	Details
Warning	LNK4272	library machine type 'x86' conflicts with target machine type 'x64'	Project2	C:\Users\rooth\OneDrive\Documents\libpcap-dev\Lib\wpcap.lib	1

I thought I added libpcap to the project properly, I'm at a loss.

[2kaud]

Which compiler are you using as there is now no requirement for main() to explicitly return a value (this only applies to main - other functions must return an appropriate value)? If an explicit value return is not provided then a return value of 0 is used.

The last error provides a clue. The machine type of the .lib must match the machine target of the project. In this case the .lib file is for x86 and your project is for x64. Try changing the target of your program to x86.

[dellthinker]

Which compiler are you using as there is now no requirement for main() to explicitly return a value (this only applies to main - other functions must return an appropriate value)?

Visual C++ 2022. I got this code from here. I wanna get the first to compile as I learn how to code with npcap. trying to compile this causes this error after adding libpcap to the project settings.

[dellthinker]

> I got the error: 'main': function must return a value on line 69.

So just add this to the end of main
return 0;

EDIT:
Also this doesn't work, it gives the same error building. Altering this code messes it up.

[salem_c]

No, fixing the compiler error exposed the linker errors.

List from the SDK

        0  2025-01-21 10:58   Lib/
        0  2025-01-21 10:58   Lib/ARM64/
    10166  2025-01-21 10:18   Lib/ARM64/Packet.lib
    26362  2025-01-23 12:03   Lib/ARM64/wpcap.lib
    10360  2025-01-17 17:33   Lib/Packet.lib
    26940  2025-01-23 12:02   Lib/wpcap.lib
        0  2025-01-21 10:58   Lib/x64/
    10166  2025-01-21 10:18   Lib/x64/Packet.lib
    26362  2025-01-23 12:03   Lib/x64/wpcap.lib

Point your project to x64/wpcap.lib

[natashasturrock]

Ah, I see what?s happening. That error is coming from the fact that your main() function is declared to return an int, but in some code paths, there?s no return statement at the end.

In your snippet, you have a return; inside the if (i == 0) block. But return; alone is only valid for functions returning void. Since your main() is int main(), every possible path through the function must return an integer. That?s why the compiler complains.

The fix is simple conceptually: make sure every exit point of main() returns an integer, usually return 0; for successful completion or another integer for errors.

Also, minor note: exit(1); works too, but using return consistently can make the compiler happier and more portable.

If you want, I can explain exactly where to put the return statements in your snippet so it compiles cleanly without changing the logic. Do you want me to do that?

[2kaud]

Ah, I see what?s happening. That error is coming from the fact that your main() function is declared to return an int, but in some code paths, there?s no return statement at the end.

In your snippet, you have a return; inside the if (i == 0) block. But return; alone is only valid for functions returning void. Since your main() is int main(), every possible path through the function must return an integer. That?s why the compiler complains.

The fix is simple conceptually: make sure every exit point of main() returns an integer, usually return 0; for successful completion or another integer for errors.

Also, minor note: exit(1); works too, but using return consistently can make the compiler happier and more portable.

If you want, I can explain exactly where to put the return statements in your snippet so it compiles cleanly without changing the logic. Do you want me to do that?

Good catch!

[dellthinker]

If you want, I can explain exactly where to put the return statements in your snippet so it compiles cleanly without changing the logic. Do you want me to do that?

Yes I would much appreciate help. These example codes are from another program I think like you explained. There's no way to really start. >_<

[2kaud]

Something like this:

int main()
{
    pcap_if_t* alldevs;
    pcap_if_t* d;
    int i = 0;
    char errbuf[PCAP_ERRBUF_SIZE];

    /* Retrieve the device list from the local machine */
    if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING,
        NULL /* auth is not needed */,
        &alldevs, errbuf) == -1)
    {
        fprintf(stderr,
            "Error in pcap_findalldevs_ex: %s\n",
            errbuf);
        return 1;    /* CHANGE HERE*/
    }

    /* Print the list */
    for (d = alldevs; d != NULL; d = d->next)
    {
        printf("%d. %s", ++i, d->name);
        if (d->description)
            printf(" (%s)\n", d->description);
        else
            printf(" (No description available)\n");
    }

    if (i == 0)
    {
        printf("\nNo interfaces found! Make sure Npcap is installed.\n");
        return 2;   /*CHANGE HERE*/
    }

    /* We don't need any more the device list. Free it */
    pcap_freealldevs(alldevs);
/*DON'T NEED RETURN HERE AS ASSUMES RETURN 0 AT MAIN FUNCTION END*/
 }

[dellthinker]

Something like this:

int main()
{
    pcap_if_t* alldevs;
    pcap_if_t* d;
    int i = 0;
    char errbuf[PCAP_ERRBUF_SIZE];

    /* Retrieve the device list from the local machine */
    if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING,
        NULL /* auth is not needed */,
        &alldevs, errbuf) == -1)
    {
        fprintf(stderr,
            "Error in pcap_findalldevs_ex: %s\n",
            errbuf);
        return 1;    /* CHANGE HERE*/
    }

    /* Print the list */
    for (d = alldevs; d != NULL; d = d->next)
    {
        printf("%d. %s", ++i, d->name);
        if (d->description)
            printf(" (%s)\n", d->description);
        else
            printf(" (No description available)\n");
    }

    if (i == 0)
    {
        printf("\nNo interfaces found! Make sure Npcap is installed.\n");
        return 2;   /*CHANGE HERE*/
    }

    /* We don't need any more the device list. Free it */
    pcap_freealldevs(alldevs);
/*DON'T NEED RETURN HERE AS ASSUMES RETURN 0 AT MAIN FUNCTION END*/
 }

I managed to get this to build. I had to add to follow the directions from here. Thanks for the help!

[natashasturrock]

You are getting the error because your main function is defined to return int, but it does not return a value at the end. Just add a return 0; before teh closing brace so the compilor knows the program finished successfully.

[2kaud]

You are getting the error because your main function is defined to return int, but it does not return a value at the end. Just add a return 0; before teh closing brace so the compilor knows the program finished successfully.

main() doesn't require a return at the end of the function. If there is no return at the end then return 0 is assumed. This only works for main(). The original error was that there was a return without value within the body of the function.

[dellthinker]

The npcap source code will not run unless you install the executable provided on their website. saying that leads me to believe that they expect developers to use it. Digging through it there are a lot of .bat files that make up a .dll that the above source I pasted needs to execute even after successfully building.