Declaring and initializing a variable in a Conditional or Control statement in C++

Question

In Stroustrup\'s The C++ Programming Language: Special Edition (3rd Ed), Stroustrup writes that the declaration and initialization of variables in the conditionals

Answer 1

While you can use a declaration as a boolean expression, you cannot place a declaration in the middle of an expression. I cannot help thinking that you are mis-reading what Bjarne is saying.

The technique is useful and desirable mostly for control variables of for loops, but in this instance I believe is ill-advised and does not serve clarity. And of course it does not work! ;)

if(   =  ) // valid, but not that useful IMO

if( (  = )   )  // not valid

for(   = ; 
     ; 
      )  // valid and desirable

In your example you have called a function with side effects in a conditional, which IMO is a bad idea regardless of what you might think about declaring the variable there.