Understanding the algorithm of Visual C++'s rand() function

Question

In C/C++, rand() and srand() are usually used by us when we want to get a random integer. But when I tried to rewrite it myself, I found it difficu

Answer 1

Prior to calling rand, since the man page for srand indicates that "If no seed value is provided, the rand() function is automatically seeded with a value of 1", then a better approach to invoking rand is to first invoke srand which will "set its argument as the seed for a new sequence of pseudo-random integers to be returned by rand()".

As an example, consider the following awk, nawk, gawk code which is used in a bash shell script to create a new (random) mac address - i.e. .genmacaddr referenced in code snippet:

enter code here
BEGIN {
     n0 = "00"
     srand()
     n1 = sprintf("%02x", int(255 * rand()))
     n2 = sprintf("%02x", int(255 * rand()))
     n3 = sprintf("%02x", int(255 * rand()))
     n4 = sprintf("%02x", int(255 * rand()))
     n5 = sprintf("%02x", int(255 * rand()))
     print n0":"n1":"n2":"n3":"n4":"n5
}

where the code snippet in the bash shell script is:

enter code here
ifconfig eth0 down
newmacaddr=`nawk -f .genmacaddr -`
ifconfig eth0 hw ether $newmacaddr
ifconfig eth0 up

If I am not mistaken, the seed value for srand is derived from the system clock.

I hope this helps you to understand an approach to your coding solution that will work.