c++ - what's wrong with declaring a variable inside if's condition? -

c++ - what's wrong with declaring a variable inside if's condition? -

perhaps getting rusty (have been writing in python recently).

why not compile?

if ( (int i=f()) == 0)

without () around int i=f() another, much more reasonable error of i not beingness boolean. that's why wanted parentheses in first place!

my guess using parentheses makes expression, , declaration statements not allowed in expression. so? , if yes, 1 of c++'s syntax quirks?

btw, trying this:

if ( (mymap::iterator = m.find(name)) != m.end()) homecoming it->second;

you can declare variable in if statement in c++ restricted used direct initialization , needs convert boolean value:

if (int = f()) { ... }

c++ doesn't have described "declaration expression", i.e. [sub-] expressions declaring variable.

actually, looked clause in standard , both forms of initialization supported according 6.4 [stmt.select] paragraph 1:

... condition: look attribute-specifier-seqopt decl-specifier-seq declarator = initializer-clause attribute-specifier-seqopt decl-specifier-seq declarator braced-init-list ...

that is, possible write:

if (int i{f()}) { ... }

obviously, works in c++2011 because c++2003 doesn't have brace-initialization.

c++ syntax variable-declaration