Const char* and char*, string constants

notes ： When it comes to strings , Basically string constants .

See such a sentence ： mention const char*, Think that this pointer points to a string .

According to the previous understanding of constant pointer and pointer constant ,const char* p, That is, the pointer points to a constant , The value cannot be modified by a pointer . That is to say *p=XXX, Is the wrong usage .

Why? const char* It is used for strings , Because this is a constant pointer , Strings are constants , And it is stored in the constant storage area managed by the system , The compiler is not authorized to modify it . And again char Pointer to type , Or a constant pointer , Naturally, it can be associated with strings .

Another question :const char* and char* What's the difference ：

Please see the following procedure for details ：

#include<stdio.h>
#include<string.h>


int main(int argc,char* agrv[])
{
	
	printf("1. So far, normal execution ");
	const char* c = "abc";// It means that the value of the string cannot be modified through the pointer 

	char* s = "abc";
	 Pay attention to the following explanation ：
	
	s Is a string constant “abc” The pointer to , Let's see if it can be modified “abc”？
	 It should not be . because “abc” Is a constant , Put it in the constant storage area , This memory 
	 The compiler has no rights to manage , It is managed by the system ,“abc” It cannot be modified by pointer .
	 As can be seen from the above , When targeting string variables ,const char* s =“abc”  and char* s=“abc” It's essentially the same thing ,
	 Are pointers to constant storage areas managed by the system . although   There is no error in trying to change the syntax of the string content through the constant string pointer , But in fact, the program can't run ,
	 This explanation , The program is compiled , It doesn't mean there's no problem when it runs .
	 about const char* s, This is more standardized , The compiler can directly check syntax errors .

	 So if you need to define a constant that points to a string （ Form like “abc”, Or single character “a”, Such character constants ） The pointer of , The standard writing is const char*  The form of the variable name .
	 It's written in char*  Variable names can also , It's just like const char*  The variable name is the same , however const char*  Variable name   Is a more standardized way of expression .
	
	
	printf("%p\n", s);

	*(s+1) = "d";// Try to modify by pointer “abc” The elements in , There is no error in the statement ,
	 But the program can no longer run at this stage , Because this operation is illegal , Although there is no grammatical error .

	printf("2. So far, normal execution ");

	printf("%s\n", s); The program can't run , No output 
	
	*(c + 1) = "d"; Prompt syntax error directly , The program cannot be compiled without commenting it out 
	
	
	printf("%s\n", *c);

	
	return 0;
}

From the above analysis, we can see that , When pointing to a string （ Constant ） when ,const char* and char* There is no difference , however const char* It can pass more clearly const Remind you that you cannot modify constant strings through pointers ,char* Nor can string constants be modified , But what is not shown is written const, Both are the same in use .

about char*, If you want to modify string constants only , There is no mistake in grammar , Compilation can also pass , But there will be problems when the program runs .

Reference resources const char* str="abcd" And char* str="abcd" Is there a difference ？-CSDN Forum