Why would you use an assignment in a condition?
It's more useful for loops than if statements.
while(var = GetNext())
{
...do something with 'var'
}
Which would otherwise have to be written
var = GetNext();
while(var)
{
...do something
var = GetNext();
}
I find it most useful in chains of actions which often involve error detection, etc.
if ((rc = first_check(arg1, arg2)) != 0)
{
report error based on rc
}
else if ((rc = second_check(arg2, arg3)) != 0)
{
report error based on new rc
}
else if ((rc = third_check(arg3, arg4)) != 0)
{
report error based on new rc
}
else
{
do what you really wanted to do
}
The alternative (not using the assignment in the condition) is:
rc = first_check(arg1, arg2);
if (rc != 0)
{
report error based on rc
}
else
{
rc = second_check(arg2, arg3);
if (rc != 0)
{
report error based on new rc
}
else
{
rc = third_check(arg3, arg4);
if (rc != 0)
{
report error based on new rc
}
else
{
do what you really wanted to do
}
}
}
With protracted error checking, the alternative can run off the RHS of the page whereas the assignment-in-conditional version does not do that.
The error checks could also be 'actions' — first_action()
, second_action()
, third_action()
— of course, rather than just checks. That is, they could be checked steps in the process that the function is managing. (Most often in the code I work with, the functions are along the lines of pre-condition checks, or memory allocations needed for the function to work, or along similar lines).