String knowledge note in C

String knowledge note in C
1: In C, we say "H" is a string with two bytes in total, followed by a '\ 0' pseudo zero Terminator.

'H' is a number. Verify with the following program.

#include <stdio.h>int main(void){printf("%d %d\n",sizeof("c"),sizeof('s'));}

2: String creation process

#include <stdio.h>int main(void){char * p = "hello world!";printf("%s\n", p);}

Here, Why can a string be assigned to a char * type pointer variable?
1: When we write hello, it tells the compiler to store 6 bytes in the read-only data segment.
2: the value of the "hello" expression represents the address of the first character of the string.

# Include <stdio. h> int main (void) {char * p = "world"; // you can see from the code that the string represents an address. Printf ("% s \ n", p); printf ("% c \ n", * ("hello"); return 0 ;}

// When the output data exceeds the threshold, the output data increases. # include <stdio. h> void func (void) {int * p = "hello! "; Write (1, p, 10);} int main (void) {int * q =" hello world "; func (); return 0 ;}

3: Passing parameters in the string:

#include <stdio.h>int main(void){char * p = "hello word! %d\n";printf(p,5);return 0;}

4: Modify the string content

# Include <stdio. h> int main (void) {char * p = "hello word! \ N "; p [0] = 'H'; // This will cause compilation problems, because the content of the read-only data segment cannot be changed to printf (" % c \ n ", p [0]); // printf (p, 5); return 0 ;}

// If we want to modify the content in the read-only string, we need to put the data in an array, which is equivalent to copying the content in the read-only data segment.


For example

#include <stdio.h>#include <string.h>int main(void){        char * p = "hello world!";        char ch[64];        strcpy(ch,p);        ch[0]='H';        printf("%s\n",ch);        return 0;}

5: Evaluate the valid byte length of a string:

# Include <stdio. h> # include <string. h> int main (void) {char * p = "hello"; // p [0] = 'H'; // printf ("% c \ n ", p [0]); // printf (p, 5); char a [] = "hello"; // strlen () this function is used to evaluate the valid byte length of a string. printf ("% ld \ n", strlen (a); return 0;} is determined based on the pseudo-zero end time ;}