C traps and defects Chapter 3 semantic "traps" 3.4 avoid "couple method"

avoid “ Couple lifting method ”
“ Couple lifting method ”（synecdoche） It is a means of literary rhetoric , It's a little similar to expressing joy with a smile 、 Approval , Or metaphorically express the relationship between the referent and the referent . stay 《 Oxford English dictionary 》 in , Yes “ Couple lifting method ”（synecdoche） That's how it's explained ：“ Replace the relatively narrow words with broader words , Or vice versa ; for example , The whole represents the part , Or part represents the whole , To represent biological species by biological classes , Or to represent biological classes with biological species , wait .”
C A common language “ defects ”： Confuse the pointer with the data pointed to by the pointer . In the case of strings . Programmers often make such mistakes .
for example ： 
char *p, *q;
p = "xyz";
The above assignment statement makes p The value of is a string "xyz", However, this is not the case , It is particularly important to remember this . actually ,p The value of is a point with 'x'、'y'、'z' and '\0' this 4 Pointer to the starting element of an array of characters . therefore , If we execute the following statement ： 
q = p;
p and q Now there are two pointers to the same address in memory . This assignment statement does not copy characters in memory at the same time .
Here's the thing to remember , The assignment pointer does not copy the data pointed to by the pointer at the same time .
therefore , When we execute the following statement ： 
q[1] = 'Y';
q The memory referred to now stores strings 'xYz'. because p and q It points to the same memory , therefore p Of course, what is stored in the memory pointed to is also a string 'xYz'.
Translation notes ：ANSI C The standard stipulates that string literal Make changes .K&R C The explanation of this problem in is , The behavior of trying to modify a string constant is undefined . some C The compiler also allows q[1]='Y' This modification behavior , Such as LCC v3.6. however , This kind of writing is not worth advocating .