Analyze strcpy Functions

 

The analysis of these Interview Questions contains strong interests. Find out the errors:

Question 1:

Void test1 () { Char string [10]; Char * str1 = "0123456789 "; Strcpy (string, str1 ); }

Question 2:

Void test2 () { Char string [10], str1 [10]; Int I; For (I = 0; I <10; I ++) { Str1 [I] = 'a '; } Strcpy (string, str1 ); }

Question 3:

Void test3 (char * str1) { Char string [10]; If (strlen (str1) <= 10) { Strcpy (string, str1 ); } }

Answer:

Question 1 string str1 requires 11 bytes to be stored (including '\ 0' at the end), while string only has 10 bytes of space, strcpy will cause the array to cross-border;

For question 2, if the subject points out that the character array str1 cannot end in the array, it can give 3 points; if the subject points out strcpy (string, str1) calling makes the number of bytes replicated from the str1 memory to the string memory uncertain. It can be given 7 points. Based on this, it is pointed out that the strcpy function is working for 10 points;

For question 3, if (strlen (str1) <= 10) should be changed to if (strlen (str1) <10 ), the result of strlen does not count the 1 byte occupied by '\ 0.

Analysis:

Measure the test taker's knowledge about basic skills:

(1) The string ends with '\ 0;

(2) sensitivity to array out-of-bounds control;

(3) how the database function strcpy works. If the total score of a standard strcpy function is 10, the following are several different answers:

2 points Void strcpy (char * strDest, char * strSrc) { While (* strDest ++ = * strSrc ++ )! = '\ 0 '); } 4 points Void strcpy (char * strDest, const char * strSrc) // Add the source string to const, indicating that it is an input parameter and adds 2 points { While (* strDest ++ = * strSrc ++ )! = '\ 0 '); } 7 points Void strcpy (char * strDest, const char * strSrc) { // Add non-0 assertions to the source and target addresses, and add 3 points Assert (strDest! = NULL) & (strSrc! = NULL )); While (* strDest ++ = * strSrc ++ )! = '\ 0 '); } 10 points // For chained operation, add 3 points to return the destination address! Char * strcpy (char * strDest, const char * strSrc) { Assert (strDest! = NULL) & (strSrc! = NULL )); Char * address = strDest; While (* strDest ++ = * strSrc ++ )! = '\ 0 '); Return address; }

We can clearly see from two to ten answers that the little strcpy has hidden so many xuanjicang! What a solid basic skill is required to write a perfect strcpy!