Lvalue to Rvalue conversions

Question

From 4.1/2

The value contained in the object indicated by the lvalue is the rvalue result. When an lvalue-to-rvalue conversion occurs within the operand of sizeof (5.3.3) the value contained in the referenced object is not accessed, since that operator does not evaluate its operand.

Out of curiosity, I was wondering, does the same applies to the if, for, while statements, i.e lvalue is converted to rvalue when the result of statement is evaluated?

score 7 · Accepted Answer · edited May 23 '17 at 10:30

7

Yes. Without lvalue-to-rvalue conversion, it cannot read it's value.

Loosely speaking, think of lvalue as some sort of container, and rvalue as the value contained in the container.

C++03, section §3.10/7 reads,

Whenever an lvalue appears in a context where an rvalue is expected, the lvalue is converted to an rvalue; see 4.1, 4.2, and 4.3.

Read it along with, §4.1/2 (your quotation),

The value contained in the object indicated by the lvalue is the rvalue result.

Related topic:

What standard clause mandates this lvalue-to-rvalue conversion?

edited May 23 '17 at 10:30

Community

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answered Sep 18 '11 at 08:44

Nawaz

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In terms of standard, Does it mean that it 'lexically contains an rvalue'?. I remember reading it but i'm not sure if i'm getting it right. – parc84 Sep 18 '11 at 08:55
@parc84: Added quotation from the spec. – Nawaz Sep 18 '11 at 09:02

score 3 · Answer 2 · answered Sep 18 '11 at 09:10

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The answer is yes.

When a bool rvalue is expected, the conversion also is applied. Let test be a variable to see an example:

if( test )

Rvalue of test, true or false, is evaluated inside the if.

answered Sep 18 '11 at 09:10

robermorales

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Lvalue to Rvalue conversions

2 Answers2