The difference between single and double quotes in C language (solve the puzzle of extracting IP address from string) _c language

Problem:
After converting std:string to char* from a C + + file, the char* containing the IP address needs to be extracted from the IP address in the string char*;

Solution:
1. Solution Idea:
The maximum IP address is 12 characters + 3 periods = 15 characters, the general expression is 192.168.111.111;
Can be parsed from the first character when it is not '. ' , save all the characters and convert all the saved characters to 16.

2. The procedure is as follows:

Copy Code code as follows:

typedef struct {
Char addr_ipv4[4];
} Ipaddr_ipv4;
#include <stdlib.h>
Function:to extract HEX value of IP address from string expression.
Ipaddr_ipv4 parse_ipstring (const char *STR, U8 strlen) {
Ipaddr_ipv4 IPv4;
Char Tmpbuf[4] = {0};
U8 K;
U8 inx = 0;
U8 j = 0;
dprintf ("The Ch_ip is:%s\n", ch_ip);
For (k=0 k<strlen; k++) {
if (Str[k]!= '. ') {
dprintf ("K-inx:%d\n", K-inx);
memcpy (&tmpbuf[k-inx], &str[k], 1);
}
else {
Inx = k + 1;
dprintf ("Inx:%d, Tmpbuf:%s\n", Inx, Tmpbuf);
Ipv4.addr_ipv4[j++] = Strtol (Tmpbuf, NULL, 10);
memset (tmpbuf, 0, sizeof (TMPBUF));
Continue
}
dprintf ("Tmpbuf:%s\n", tmpbuf);
IPV4.ADDR_IPV4[J] = Strtol (Tmpbuf, NULL, 10);
}
dprintf ("IPv4 is:");
for (k=0; k<sizeof (Ipv4.addr_ipv4); k++) {
dprintf ("%d", ipv4.addr_ipv4[k]);
// }
dprintf ("\ n");
return IPv4;
}

The application is as follows:

Copy Code code as follows:

char* ch_ip = NULL;
Ipaddr_ipv4 ipv4addr;
Ch_ip = (char*) malloc (16);
memset (ch_ip, 0, 16);

Parse IP Address
Ch_ip = Getipaddr ();

Convert IP address from string to HEX expression
IPV4ADDR = parse_ipstring (Ch_ip, strlen (CH_IP));

3. Attention MATTERS:
The original character is compared with the IF (Str[k]!= "." Instead of if (Str[k]!= '. '), the result has been wrong.
Then repeatedly find the reason, only to know the difference between single quotes ' and double quotes ' ":

(1). Meaning is different.
A character enclosed in single quotes represents an integer that corresponds to the sequence value of the character in the ASCII character set;
Double quotes result in strings, even if only one character is a string, and a character in double quotes represents a pointer to the starting character of an unnamed array;
For example: '. ' Represents decimal 46, hexadecimal 0x2e;
and "." Represents a pointer to the starting character "." A pointer to an array of;

(2). Different sizes.
Single quotes cause a character size to be a byte;
A character size that is caused by double quotes is two bytes, because a string of double quotes adds a 0x00 at the end of the string as the end identity of the string.

The IP address is correctly taken in my program.
Solve the problem.