Pointer learning diary (V) classic abstract data types and standard function libraries

Abstract data types （ADT） yes C An indispensable tool for programmers , This is determined by their attributes .
This kind of ADT Linked list , Stack , queue , Trees, etc .

Memory allocation ：
all ADT Need to determine one thing —— How to get memory to store values . Yes 3 Two options ：
1. Static array ： Fixed length , The simplest
2. Dynamically allocated arrays ： The length of the array can be determined at runtime . If necessary , You can assign a new and larger array , Then copy the original array elements to the new array , Then delete the original array , So as to dynamically change the length of the array .
3. The chain structure of dynamic allocation ： Provides maximum flexibility , There is almost no limit to the number of elements in this way , But the linked fields of chain structure need to consume a certain amount of memory , Accessing a specific element in a chain structure is not as efficient as an array .

The above content basically involves the data structure , Dynamic allocation is undoubtedly closely related to pointers , There are only three categories described here . But there is no doubt that , Learning pointers can better understand such structures .

The standard function library is a toolbox , Greatly expanded C The power of programmers . Although later C++ Appearance , bring C Some function libraries of the language have changed , But in general, it hasn't changed much , Here it is , Write some function libraries that I think are more interesting .

Character conversion <stdlib.h>
int atoi(char const string);
long int atol(char const string);
long int strtol(char const* string,char **unused,int base);

atoi and atol almost , It is to convert a string into a number , Only the former returns int Type the latter returns long int type .
strtol() Medium base Is decimal , Such as 12 Express 12 Base number ,10 Express 10 Base number .
if base16 Base so “a,b,c,d,e,f” Is a legal character .
for example x=strtol(" 590bear",next,12);
x The value of is 9947, First ,590b It's a legal character , because 12 Base number , therefore b It is also a legal character .
then e It's illegal characters , This is the end of the program , take e Deposit to next In the variable you point to .

Processor time <time.h>
clock_t clock(void);
Returns the time consumed by the processor since the program began to execute