#language-lawyer

[goodanswerbiz]

Fixed Is the operation "false < true" well defined? #dev #it #asnwer

Fixed Is the operation "false < true" well defined? #dev #it #asnwer

Is the operation "false < true" well defined?

Does the C++ specification define:

the existence of the ‘less than’ operator for boolean parameters, and if so,

the result of the 4 parameter permutations?

In other words, are the results from the following operations defined by the specification?

false < false false < true true < false true < true

On my setup (Centos 7, gcc 4.8.2) , the code below…

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[sevennet-blog]

How to: Is it safe to push_back an element from the same vector?

How to: Is it safe to push_back an element from the same vector?

Is it safe to push_back an element from the same vector?

vector<int> v; v.push_back(1); v.push_back(v[0]);

If the second push_back causes a reallocation, the reference to the first integer in the vector will no longer be valid. So this isn’t safe?

vector<int> v; v.push_back(1); v.reserve(v.size() + 1); v.push_back(v[0]);

This makes it safe?

Answer: Is it safe to push_back an element from the…

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[goodanswerbiz]

Fixed int a = {1,2,}; Weird comma allowed. Any particular reason? #dev #it #asnwer

Fixed int a = {1,2,}; Weird comma allowed. Any particular reason? #dev #it #asnwer

int a[] = {1,2,}; Weird comma allowed. Any particular reason?

Maybe I am not from this planet, but it would seem to me that the following should be a syntax error:

int a[] = {1,2,}; //extra comma in the end

But it’s not. I was surprised when this code compiled on Visual Studio, but I have learnt not to trust MSVC compiler as far as C++ rules are concerned, so I checked the standard and it isall…

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[goodanswerbiz]

Fixed Can C++ code be valid in both C++03 and C++11 but do different things? #dev #it #asnwer

Fixed Can C++ code be valid in both C++03 and C++11 but do different things? #dev #it #asnwer

Can C++ code be valid in both C++03 and C++11 but do different things?

Is it possible for C++ code to conform to both the C++03 standard and the C++11 standard, but do different things depending on under which standard it is being compiled?

Answer: Can C++ code be valid in both C++03 and C++11 but do different things?

I point you to this article and the follow-up, which has a nice example of how

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[sevennet-blog]

How to: Is "else if" a single keyword?

How to: Is "else if" a single keyword?

Is "else if" a single keyword?

I am new to C++. I often see conditional statement like below:

if statement_0; else if statement_1;

Question:

Syntactically, shall I treat else if as a single keyword? Or is it actually an nested if statement within the outer else like below?

if statement_0; else if statement_1;

Answer: Is "else if" a single keyword?

No, it is not. They are two keywords and,…

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[sevennet-blog]

How to: A positive lambda: '+{}' - What sorcery is this?

How to: A positive lambda: '+{}' – What sorcery is this?

A positive lambda: ‘+[]{}’ – What sorcery is this?

In Stack Overflow question Redefining lambdas not allowed in C++11, why?, a small program was given that does not compile:

int main() { auto test = []{}; test = []{}; }

The question was answered and all seemed fine. Then came Johannes Schaub and made an interesting observation:

If you put a +before the first lambda, it magically starts to work.

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[sevennet-blog]

How to: Is the operation "false < true" well defined?

How to: Is the operation "false < true" well defined?

Is the operation "false < true" well defined?

Does the C++ specification define:

the existence of the ‘less than’ operator for boolean parameters, and if so,

the result of the 4 parameter permutations?

In other words, are the results from the following operations defined by the specification?

false < false false < true true < false true < true

On my setup (Centos 7, gcc 4.8.2) , the code below…

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[sevennet-blog]

How to: Why is f(i = -1, i = -1) undefined behavior?

How to: Why is f(i = -1, i = -1) undefined behavior?

Why is f(i = -1, i = -1) undefined behavior?

I was reading about order of evaluation violations, and they give an example that puzzles me.

1) If a side effect on a scalar object is un-sequenced relative to another side effect on the same scalar object, the behavior is undefined.

// snip f(i = -1, i = -1); // undefined behavior

In this context, i is a scalar object, which apparently means

Arit…

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