For loop condition (cpp)

Question

for (; cnt--; dp += sz)
{
        pair_sanitize_struct(rec_id, ctx->api_mode, dp, FALSE);
}

Could some one explain how this for loop works? It belongs to a cpp file. I dont understand the condition in the for loop and how it is being checked. (The function is being invoked)

Answer 1

The general form of for statement looks like this:

for (init-statement; condition; expression)
    statement

init-statement is used to initialize or assign a starting value that is modified over the course of the loop. condition serves as the loop control. As long as condition evaluates as true, statement is executed. expression is evaluated for each iteration only if condition is true

Back to your code:

for (; cnt--; dp += sz)

init-statement here is a null statement that does nothing. condition is cnt-- which evaluates its value as cnt then decrements 1. If cnt is non-zero, condition is true, if cnt is zero, condition is false.