[Cadvanced] 14, single quotes and double quotes

Summary

single quotation mark in C language is used to represent the character literal of ; the character literal is essentially an integer;

2) C language double quotation marks to indicate string literal; string literals is essentially a pointer (memory address);

3) 0x08048000 segmentation fault (the accessible address value needs to be greater than or equal to this value, 32-bit system);

4) Note: char type and char* type should be with correct literal for 1614f175290305; although char a = ""; char* s ='a'; can be compiled, but it will be out when used Unexpected .

5) The confusion between character literals and string literals can be edited in the C compiler, but you should pay attention to . In the 1614f17529031b project, all warnings must be treated as errors.

Single and double quotes

C language single quotes used to represent character literals; nature character literal is an integer, 'a' is 1 byte in memory, 'a' + 1 denotes 'a' ASCII value Add 1, and the result is'b'.

double quotation marks in the C language are used to represent the string literal; the essence of the string literal is a memory address (address value), "a" occupies 2 bytes in the memory, and "a"+1 represents a pointer Operation, the result points to the terminator'\0' in "a".

• Code reading:

  char* p1 = 1;
  char* p2 = '1';
  char* p3 = "1";
  
  printf("%s, %s, %s", p1, p2, p3);
  
  printf('\n');
  printf("\n");

  Code analysis:

  p1 用一个整数字面量1进行初始化，有warning，但可以编的过，因为指针本质也是一个32(64)位的整数值
  p2 用一个字符字面量'1'进行初始化，同p1。字符'1'本质也是一个整数，值为49
  p3 用一个字符串字面量"1"进行初始化，字符串字面量的本质是一个指针（内存地址），没有问题
  
  printf(param1, ...)的第一个参数是一个指针，地址值
  printf('\n')可以编的过，但是warning，同p2，使用10作为一个地址值传给printf函数
  printf("\n")可以编的过，使用一个字符串字面量作为参数，换行
  
  综上：p1 p2 printf('\n')都是可以编的过，但是有问题的语句，在进行打印的使用就会段错误，
  因为使用了错误的地址值，访问了不该访问的内存，野指针！！！

  

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• Code reading:

    char c = " ";
  
    while(c == "\t" || c == " " || c == "\n")
    {
        scanf("%c", &c);
    }
  

  Code analysis:

  c的初始化：使用一个只有空格字符的字符串字面量进行初始化；实际上是用一个指针（内存地址值）进行初始化
  由于char类型占1个字节，指针类型占4字节（32位），所以会发生截断
  再去进行while循环的判断，第一次就为false，不会进到循环中
  
  所以要正确判断字符类型和字符串类型，确保使用的类型是正确的：
  修改，将"\t"等都改成'\t'。

This article is summarized from "C Language Advanced Course" by Tang Zuolin from "Ditai Software Academy".
If there are any errors or omissions, please correct me.