Value of Do{}while (0) When macro definition (#define) in C language (GO)

Value of Do{}while (0) When macro definition (#define) in C language

Recently found in the code of the new company everywhere used do{...} while (0), Google a bit, found that stack overflow early on a lot of discussion, summed up the discussion, coupled with their own understanding, do{...} while (0) the value is mainly reflected in:

1. Increase the adaptability of the Code

The following macro definition does not use do{...} while (0)

#define FOO (x) foo (x); Bar (x);

Such a macro definition will not have problems with separate calls, such as:

FOO (+)

After the macro expands, it becomes:

1	foo(x);bar(x);

This calls Foo without any problems, but Foo (x) cannot be placed in a control statement, such as

1234	if(condition)    FOO(x);else    ...;

After the macro is expanded, it becomes

If (condition)    foo (x); bar (x);  else     ...;  

This leads to grammatical errors , syntax errors are not scary, in the compilation phase can be found, the more deadly is that he may lead to logic errors , this error compiler can not find that the problem, the programmer is crazy. For example:

If (condition)    FOO (x);

This code has been expanded to become:

If (condition)    foo (x); bar (x);

This will be called regardless of whether condition is true or False,bar (x). Are there any brothers who have been tortured by this?

This time do{...} while (0) the value is reflected, modify the definition of Foo

#define FOO (x) do {foo (x), bar (x);} while (0)

So foo, put in the control statement there is no problem.

Maybe someone said, "Put Foo (x); bar (x) in curly braces?" For example, this defines:

#define FOO (x) {foo (x); bar (x);}

Then look at the following code:

If (condition)    FOO (x);  else     ...;  

After expansion:

If (condition)    // Note the last semicolon, syntax error else ...;    

Still grammatical error;

2. Increase the extensibility of the Code

I understand that extensibility, mainly in macro definitions, can also refer to other macros, such as:

#define FOO (x) Do{other_foo (x)} while (0)

So we don't have to worry about Other_foo. But the statement or the statement, there is no problem

3. Increase the flexibility of the Code

The flexibility is mainly in that we can break out of a macro, such as the following definition:

#define FOO (x)  do{\    FOO (x);      if(condition (x)) break         ; bar (x) ...
} while (0)

Value of Do{}while (0) When macro definition (#define) in C language (GO)