CODEWITHSUNDEEP
c++if-statement
MoonKnight
MoonKnight

Reputation: 23831

Multiline Formatting of else Statements in C/C++ without Braces

I am rewriting some C++ code, I have the following 

if (ConfidenceBias.value > 0) *normalInfo = tree.setDataField(NormalSigs(), *samples, *sampleData, density, pointWeightSum, ConversionAndBiasFunction);
else *normalInfo = tree.setDataField(NormalSigs(), *samples, *sampleData, density, pointWeightSum, ConversionFunction); ThreadPool::Parallel_for(0, normalInfo->size(), [&](unsigned int, size_t i) { (*normalInfo)[i] *= (Real)-1.; });

I assume that this is equivalent to 

if (ConfidenceBias.value > 0) 
{
    *normalInfo = tree.setDataField(NormalSigs(), *samples, *sampleData, density, pointWeightSum, ConversionAndBiasFunction);
}
else 
{
    *normalInfo = tree.setDataField(NormalSigs(), *samples, *sampleData, density, pointWeightSum, ConversionFunction);  
}

ThreadPool::Parallel_for(0, normalInfo->size(), [&](unsigned int, size_t i) { (*normalInfo)[i] *= (Real)-1.; });

but there is a slight conern that the compiler is interpreting the original as 

if (ConfidenceBias.value > 0) 
{
    *normalInfo = tree.setDataField(NormalSigs(), *samples, *sampleData, density, pointWeightSum, ConversionAndBiasFunction);
}
else 
{
    *normalInfo = tree.setDataField(NormalSigs(), *samples, *sampleData, density, pointWeightSum, ConversionFunction);  
    ThreadPool::Parallel_for(0, normalInfo->size(), [&](unsigned int, size_t i) { (*normalInfo)[i] *= (Real)-1.; });
}

I cannot find a reference to what the VSVC compiler does anywhere. Which is it?

Upvotes: 0

Views: 86

Answers (1)

Samuel
Samuel

Reputation: 6490

AFAIK your assumption about the code is correct.

For most languages I am ware of only one statement or a compound-statement (e.g. braces) will be executed on the condition.

The 

ThreadPool::Parallel_for(0, normalInfo->size(), [&](unsigned int, size_t i) { (*normalInfo)[i] *= (Real)-1.; });

line is really really oddly hidden after the condition and I would assume this a code smell because it makes code hard to read, understand and debug.

Edit because I like complete answers: Also you actually do not need to know what VS C++ compiler is going to do here because this is defined. See Alex Allain's post about this.

Refer to the MSDN docs for this as well: https://learn.microsoft.com/en-US/cpp/cpp/statements-cpp?view=vs-2019

https://learn.microsoft.com/en-US/cpp/cpp/if-else-statement-cpp?view=vs-2019 states

Controls conditional branching. Statements in the if-block are executed only if the if-expression evaluates to a non-zero value (or TRUE). If the value of expression is nonzero, statement1 and any other statements in the block are executed and the else-block, if present, is skipped. If the value of expression is zero, then the if-block is skipped and the else-block, if present, is executed. Expressions that ...

To understand this check the definition of statement:

Expression statements cause expressions to be evaluated. No transfer of control or iteration takes place as a result of an expression statement.

The syntax for the expression statement is simply Syntax

[expression ] ;

and here is the compound statement block definition

A compound statement consists of zero or more statements enclosed in curly braces ({ }). A compound statement can be used anywhere a statement is expected. Compound statements are commonly called "blocks." Syntax

{ [ statement-list ] }

Verdict: Your assumption was valid, your fear unfounded :)

Upvotes: 3

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