trjhtr

I've written a small helper function that receives a string and checks if it translates to a valid subnet mask value (255.255.255.0 for example).

I would appreciate some peer review!

static bool isValidSubnetMask(IN char *subNetMask)

 char *str = NULL;
 char *endptr;
 int counter = 0;
 long int nChainInstance = -1;

 /*Check if string is valid*/
 if (!subNetMask 

Missing includes

#include <stdbool.h>
#include <string.h>

Other test may be needed

@Wingblade

Non-standard function

is_numeric() is not standard C library nor did I find it in Linux.

Questionable signature

I'd expect a function that checks a string's validity to cope with a const char * subNetMask. So using strtok() on the supplied subNetMask is not possible. Code needs to make a copy or otherwise assess the string.

// isValidSubnetMask(IN char *subNetMask)
isValidSubnetMask(IN const char *subNetMask)

Weak functionality

Below are 7 test cases that failed OP's code. Sample working code provided. sscanf() is a bit ponderous, yet useful as a test competitor.

bool is_numeric() // Added undefined Op's missing function.
 return true;


static bool isValidSubnetMask2(const char *subNetMask) subNetMask[n]) 
 return false;
 
 int i[4];
 sscanf(subNetMask, "%d.%d.%d.%d", &i[0], &i[1], &i[2], &i[3]);
 return i[0] <= 255 && i[1] <= 255 && i[2] <= 255 && i[3] <= 255;


void test(bool expect, const char *s) 
 char buff[99];
 strcpy(buff, s);
 bool y = isValidSubnetMask(buff);
 if (y != expect) 
 printf("Failed %d <%s>n", expect, s);
 
 y = isValidSubnetMask2(s);
 if (y != expect) 
 printf("Oops %d <%s>n", expect, s);
 


int main() 
 test(1, "255.255.255.0");
 test(1, "255.255.255.123");
 test(1, "0.0.0.0");
 test(0, "455.255.255.0");
 test(0, "255.255.255.-0");
 test(0, "255.255.255. 0");
 test(0, "2.2.5.2.3");
 test(0, "2.2.3");
 test(0, "+2.5.2.3");
 test(0, "A.5.2.3");
 test(0, "2.2.5.2.");
 test(0, "2..2.5.2");
 return 0;

Output

Failed 0 <255.255.255.-0>
Failed 0 <255.255.255. 0>
Failed 0 <2.2.5.2.3>
Failed 0 <2.2.3>
Failed 0 <+2.5.2.3>
Failed 0 <2.2.5.2.>
Failed 0 <2..2.5.2>