[C language] string, escape character and comment

Catalog

character string

Escape character

 \n

\0

\?

\'

 \"

 \\

\a

\t

\ddd

\xdd

  notes

character string

A string of characters enclosed in double quotes is a string literal , Abbreviated string .

char Is a character type , There is no string type .

But strings can be stored in character arrays ：

char arr[10] = "abcdef";

The above has opened up 7 Space of characters

[ ] You may not fill in , Automatically open up the corresponding space according to the following string content

The end of a string is a \0 Escape character , When calculating the length of a string \0 Only the end sign , No string content

arr2 Chinese characters only take up part of the space , Then there are many characters ,\0 Is the end of a string , So you should stay behind the space until you encounter \0 To terminate .

strlen Is a library function for finding the length of a string ,string length, The header file string. 

strlen Is used to obtain the effective length of the string , The closing mark '\0' Not included .

strlen The rules obtained are very simple ： From front to back , Until I met '\0' Yes, stop the detection .

Character array is not a valid string , Because there is no... In the back '\0', therefore strlen In solving the problem , After detecting valid characters , It will continue to detect backwards , Until I met '\0' Yes, it ends , So the first after uncertainty '\0' In what position .

Escape character

 \n

int main()
{
    printf("abcn");
    printf("abc\n")// A newline 
    return 0;
}

\0

int main()
{
    printf("abc0def")// Print abcdef
    printf("abc\0def")// Print abc
    return 0;
}

\?

// Three letter words 
//??) - ]
//??( - [
int main()
{
    printf("%s\n","(are you ok??)")
    // Print the results （are you ok]
    printf("%s\n","(are you ok\?\?)")
    // Print the results （are you ok??）
    // The current compiler does not support three letter words 
    return 0;
}

\'

int main()
{
    printf("%c\n",''');// Report errors 
    printf("%c\n",'\'');// Represents a character constant '
   
    return 0;
}
\"

 \"

int main()
{
    printf("abcdef");// Only strings can simplify printing directly 
    printf("a");// There can be only one character in the string 
    printf(""");// Report errors 
    printf("\""); Double quotation marks inside a string 
    return 0;
}

 \\

int main()
{
    printf("abcd\0ef");// Print the results abcd
    printf("abcd\\0ef");// Print the results abcd\0ef
    // Represents a backslash , Prevent it from being interpreted as an escape sequence character .
    
    printf("c:\test\test.c");// Print the results c:    est    est.c
    printf("c:\\test\\test.c");// Print the results c:\test\test.c
    // For path printing \\
    return 0;
}

\a

int main()
{
    printf("\a\a\a\a\a\a\a");
    // Warning characters , Beep 
    return 0;
}

\t

int main()
{
     printf("abcd\tef");
     //Tab = \t
    return 0;
}

\ddd

int main()
{
    printf("%c\n",'\130');//ddd Express 1~3 Eight octal numbers 
    // Print the results X, by 130 This octal is converted to a decimal number as ASCII The character represented by the code value 
    
    return 0;
}

character \0 Of ASCII The code value is 0

Letters are case ASCII Code value difference 32

\xdd

int main()
{
    printf("%c\n",'\x60');
    
    return 0;
}

The following is the format of the print data

//%d -  Print shaping 
//%c -  Print character 
//%s -  Print string 
//%f -  Print float Data of type 
//%lf -  Print double Data of type     
//%zu -  Print sizeof The return value of 

  notes

• Notes can sort out ideas
• Comments can explain complex code