strlen函数给出错误的值

Question

hello every one I have written code

char sentence[100]; 
scanf("%s" ,sentence); 
char * ptrs = sentence ;
printf("%d", strlen(ptrs));

suppose I enter

john is a boy

the strlen() function is giving me value 4 it stops counting after space what I should do thanks

Answer 1

That scanf will read only one word, if you do a printf you will see it. So there is nothing wrong with strlen .

Use fgets which reads a whole line:

if (! fgets(sentence, sizeof(sentence), stdin)) {
   fprintf(stderr, "error or end  of file while no characters have been read\n");
   return;
}

Answer 2

scanf("%s" ,sentence);

This will only read a string up to the next space. That means, the remaining characters, hence words after john is not read.

To get your desired output, use gets() instead.

gets(sentence);

Answer 3

fgets() instead of scanf().
scanf() takes the input to the end of the word.

Debugging Tips:

You should have been able to debug to some extent on your own. When strlen() wasn't giving correct answer, the first thing to do would be to verify your assumptions. You were assuming that sentence/ptrs had the correct value. A simple printf would have proved it wrong.