C/C ++ array boundary and assignment

Declaration: Char Buf [5]; The element is a [0] a [1] A [2] a [3] a [4]
A [5] does not belong to the Buf array. This array can store up to four characters, a [0] a [1] A [2] a [3, because the character array contains 5th a [4] characters for/0

# Include <stdio. h>
# Include <unistd. h>
# Include <string. h>

Int main ()
{
Char STR [5];
Char c = 'D ';

Strcpy (STR, "hello"); // string copy (include '/0 ')

Printf ("D: % d C: % c str: % s/n", C, C, STR );

If (C = '/0 ')
Printf ("c = '// 0'/N ");
Else
Printf ("C! = '// 0'/N ");

Return 0;
}

[Root @ localhost CPP] #./
D: 0 C: Str: Hello
C = '/0' // visible strcpy fill in the memory space of STR [5], that is, char C, with/0

The correct method is

[Root @ localhost CPP] # Cat A. C
# Include <stdio. h>
# Include <unistd. h>
# Include <string. h>

Int main ()
{
Char STR [5];
Char c = 'D ';

 Strncpy (STR, "hello", sizeof (STR)-1); // STR copy (not including '/0 ', that is, the/0 is not automatically added to the end of the source string)
//
STR [4] = '/0 ';
Printf ("D: % d C: % c str: % s/n", C, C, STR );

If (C = '/0 ')
Printf ("c = '// 0'/N ");
Else
Printf ("C! = '// 0'/N ");

Return 0;
}

[Root @ localhost CPP] #./
D: 100 C: d str: Hell
C! = '/0'

Without STR [x] = '/0'
[Root @ localhost CPP] # Cat A. C
# Include <stdio. h>
# Include <unistd. h>
# Include <string. h>

Int main ()
{
Char STR [6];
Char c = 'D ';

Strncpy(STR, "hello", sizeof (STR)-1); // STR copy ('/0 ')
//
// STR [5] = '/0'; if you do not add/0, the following garbled error will occur, and the subsequent content of variable C is unpredictable.
Printf ("D: % d C: % c str: % s/n", C, C, STR );

If (C = '/0 ')
Printf ("c = '// 0'/N ");
Else
Printf ("C! = '// 0'/N ");

Return 0;
}

[Root @ localhost CPP] #./
D: 100 C: d str: hellosd0 commandid? Jo login so stupid, jo
C! = '/0' ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;when using the strcnpy function: char array [80]; const char * src = "sdjfksdfjksdf"; Method 1 strcnpy (array, SRC, sizeof (array); array [sizeof (array) -1] = '/0'; // to avoid SRC length exceeding 80 (including'/0'), '/0' is not added at the end of the array '. this causes a buffer overflow .;;;;;;;;; Method 2; memset (array, 0, sizeof (array); strncpy (array, SRC, sizeof (array)-1 ); // in this way, since memset adds array 0, ensure that array [sizeof (array) -1] = '/0 ';;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; no problem when the SRC length is smaller than 80. Note that strncpy () does not automatically add '/0'; unless you can ensure that the SRC length does not exceed the array length, you can directly use strcpy (array, Src );