How to retrieve the result of netstat command

Question

I tried to get the list of opened ports in my PC in a c++ code.So, I want to use the DOS command netstat. I have written this line system("netstat -a") but I can't retrieve the result that it returns.

Answer 1

You can start with this code

int main() {
  char buf[10000];  
  FILE *p = _popen("netstat -a", "r");
  std::string s;
  for (size_t count; (count = fread(buf, 1, sizeof(buf), p));)
      s += string(buf, buf + count);
  cout<<s<<endl;    
  _pclose(p);  
}

Answer 2

You could use FILE *results = _popen("netstat -a"); and then read the results from results like you would from a file (e.g., with fread, fgets, etc.)

Alternatively, you could use GetTcpTable to retrieve the data you need more directly. Here's a reasonably complete example of retrieving most of the same data as netstat -a will:

#include <windows.h>
#include <iphlpapi.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#pragma comment(lib, "iphlpapi.lib")
#pragma comment(lib, "ws2_32.lib")

#define addr_size (3 + 3*4 + 1)   // xxx.xxx.xxx.xxx\0

char const *dotted(DWORD input) {
    char output[addr_size];

    sprintf(output, "%d.%d.%d.%d", 
        input>>24, 
        (input>>16) & 0xff, 
        (input>>8)&0xff, 
        input & 0xff);
    return strdup(output);
}

int main() { 
    MIB_TCPTABLE *tcp_stats;
    MIB_UDPTABLE *udp_stats;
    DWORD size = 0;
    unsigned i;
    char const *s1, *s2;

    GetTcpTable(tcp_stats, &size, TRUE);
    tcp_stats = (MIB_TCPTABLE *)malloc(size);
    GetTcpTable(tcp_stats, &size, TRUE);

    for (i=0; i<tcp_stats->dwNumEntries; ++i) {
        printf("TCP:\t%s:%d\t%s:%d\n", 
            s1=dotted(ntohl(tcp_stats->table[i].dwLocalAddr)), 
            ntohs(tcp_stats->table[i].dwLocalPort),
            s2=dotted(ntohl(tcp_stats->table[i].dwRemoteAddr)),
            ntohs(tcp_stats->table[i].dwRemotePort));
        free((char *)s1);
        free((char *)s2);
    }
    free(tcp_stats);

    return 0;
}

Note that I wrote this a long time ago -- it's much more C than C++. If I were writing it today, I'm pretty sure I'd do a fair number of things at least a little differently.