Implement strlen () function, strcmp () function const knowledge Point

1. Implementation of the strlen () function:

#include <stdio.h>int strLen (char *str); int StrLen (char *str) {int i = 0;        while (*STR) {str++;    i++; } return i;}    void Main (void) {char *str = "ABCDEFG";        int length;    Length = StrLen (str); printf ("%d\n", length);}

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2. Implementation of the strcmp () function:

 #include <stdio.h>int strcmp (char *str1, char * STR2); int strcmp (CHAR&NBSP;*STR1,&NBSP;CHAR&NBSP;*STR2) {    while (*str1 ==  *STR2&NBSP;&&&NBSP;*STR1&NBSP;&&&NBSP;*STR2) {         str1++;        str2++;    }    &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;RETURN&NBSP;*STR1&NBSP;-&NBSP;*STR2;} Void main (void) {    char *str1 =  "Hello";     char  *str2 =  "Hell";         printf ("%d\n",  strcmp (str1 , &NBSP;STR2));} 

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3, the use of const:

Const read-only.

(1) const int a = <=> int const A = 100; A space is a read-only space and the value of a space cannot be changed.

(2) const int *a;  <=> int const *A; The value of the *a cannot be changed, and the value of a pointer variable can be changed.

int* const A; The value of the *a can be changed, a pointer variable is read-only, and its value cannot be changed

const int* const A; *a, A is read-only space, and its value cannot be changed!

Const from WHO in, decorate who, who can not change!!!

Note: You just started programming with Linux (1). Linux 64-bit vs. 32-bit differences:

The int is 4 bytes. 64 bits, long 8 bytes, pointer 8 bytes

(2). Comments block under Linux: #if 0 (Note) 1 (not commented)

#endif

(3). Gcc-c only compile does not connect gcc. C-o target file compilation and connection

(4). objdump-d Test (executable file) > x86 disassembly file to view X86 content.

Compilation results often with the platform, compiler relationship is very big!!!

Implement strlen () function, strcmp () function const knowledge Point