Analyze the statement of C language from two examples

 

When reading the third chapter of "C expert programming", the book talked about the C language statement. The book "C expert programming" contains more than two hundred pages, I spent a chapter explaining this issue, which is enough to see the importance of this issue. It is far from enough to fully understand the C language statement, you need to practice more and read a lot of code written by others. The following two examples from expert C programming are used to illustrate this problem. Many of the following content is taken from page 55th-79 of Expert C programming.

In C language, the declaration form is similar to the format used. This usage may be original in C language, and K & R also acknowledges that "the syntax of C language declaration sometimes brings serious problems ". The biggest problem with C language statements is that you cannot read a statement from left to right in a natural way that people are used. The following is an example:

Char * const * (* next )();

If you can see the meaning of this statement at first glance, it proves that your C language skills have reached a certain level. The recognition steps in Expert C programming are as follows:

1) start with the variable name "next" and notice that it is directly enclosed in parentheses;

2) Let's take the things in the brackets as a whole and conclude that "next" is a pointer;

3) consider the things outside the brackets and make a choice between the asterisk prefix and the suffix of the brackets;

4) according to the priority rules declared in C Language (which will be given later), the higher priority is the function brackets on the right, so "next" is a function pointer pointing to a return... functions;

5) then, process the prefix "*" to get the content indicated by the pointer;

6) Finally, interpret "char * const *" as a constant pointer to a string.

To sum up the above results, this statement indicates "next is a pointer pointing to a function. This function returns another pointer pointing to a constant pointer of char type ". This problem was solved.

Let's look at another example:

Char * (* c [10]) (int ** p );

First, start with the variable name c, and then process the suffix "[]", indicating that c is an array, and then process the prefix "*", indicating that c is a pointer array. Then, the parentheses indicate that the pointer type in array c is a pointer to a function, and the parameter of this function has only one: a pointer to a pointer, the return value of this function is a pointer to a string. Summarized as follows:

"C is an array [0... 9]. Its element type is a function pointer, and its return value is a pointer to a string, and a pointer to the pointer is used as a unique parameter ".

The priority rules of C language declarations mentioned in Expert C programming are as follows, from page 64th.

 

 

Author Hai Zi