Confusions about argv and strncpy ()

If a problem occurs, the command line parameter is copied to the string and the printed result is inconsistent with that of the directly printed command line parameter.

I don't know where the problem is.

 

# Include <stdio. h> # Include < String . H> # Define Len 5 Int Main ( Int Argc, Char * Argv []) {  Char  S1 [Len]; Char  S2 [Len];  For ( Int I = 0 ; I <Len; I ++ ) {S1 [I] = '  \ 0  '  ; S2 [I] = '  \ 0  '  ;} Printf (  " % S \ n  "  , S1, S2 );  //  Print command line parameters directly      For ( Int I = 1 ; I <argc; I ++ ) Printf (  "  % S \ n  "  , Argv [I]);  //  Copy the command line parameter to the string and print it again. Strncpy (S1, argv [1  ], Len); strncpy (S2, argv [  2  ], Len); printf (  "  % S \ n  "  , S1, S2 );  Return   0  ;} 

 

Run:

Test.exe TMP temp

The result is correct:

TMP
Temp
TMP
Temp

However, run:

Test.exe TMP tempmoreword

Result:

TMP
Tempmoreword
TMP
Tempmtmp

that is, an error occurs when the command line parameter exceeds the string length specified by strncpy.