Problems encountered by the writing strlen function.

Today, when I realized the strlen function, I met a very interesting warning:

warning:deprecated conversion from string constant to ' char* ' [-wwrite-strings]

1#include <stdio.h>2 3 intStrlenChar*str) {4     Char*s;5      for(S=STR; *s; s++);6     returnS-str;7 }8 9 intMain ()Ten { One     Char*S1 ="ABC"; A     CharS2[] ="ABC"; -printf"%d\n", strlen (S1)); -printf"%d\n", strlen (S2)); the     return 0; -}

Since the previous contest has been avoiding pointers, it has been used to define "[]", which is the way arrays are. Now the use of "*" is defined by the way the pointer is to produce warning, for a moment still baffled its solution.

But I think, with the function of the value should be no relationship here, so I delete the code is left only the definition of the statement, and compile again.

1 #include <stdio.h>23int  main ()4{5     Char *s1  " ABC " ; 6     return 0 ; 7 }

Yes, it's just this definition statement, and the warning is still there.

A general understanding of the following warning message is that the deprecated conversion from a string constant to a char pointer? See Foggy, but think is not let write!

2  3  int   main ()  4  5  char  *s1 =  " ABC   ;  6  *s1 =  "    7  return  0   8 } 

This is going to get an error!

Error:invalid conversion from ' const char* ' to ' char ' [-fpermissive]

So, do not let the modified value, is not a constant!

So I was determined to add the const:

1 #include <stdio.h>23int  main ()4{5     Const Char *s1  "ABC"; 6     return 0 ; 7 }

The world is quiet!

But why does a string pointer have to be const-decorated?

The brain shows, it's obvious that we are assigning a string constant "ABC" address to the S1 pointer, then the S1 pointer should be received (canonical) using a const pointer.

So what do you do if you want to change it? The answer is an array:

1#include <stdio.h>2 3 4 intMain ()5 {6     Const Char*S1 ="ABC";7     CharS2[] ="111";8*S2 ='2';9printf"%s\n", S2);Ten     return 0; One}

So, this time the output value is "211".

Problems encountered by the writing strlen function.