strlen(null_terminated_array) does printf("%zu", strlen(null_terminated_array)) prints size_t that includes '\0'

Question

If I have a char *null_terminated_array="hello", I think printf("%zu",strlen(null_terminated_array)) should print 5 (not including '\0') and not 6 (including '\0').

This assumption is correct. `strlen` does not count the terminating `0` byte. Did you get different results? Then you need to show a more complete piece of code. — Gerhardh, Oct 01 '21 at 14:11
See the C++ Q&A [`sizeof` string literal](https://stackoverflow.com/q/1392200/15168) — valid for C too. See also the C standard [§7.1.1 Definition of terms](http://port70.net/~nsz/c/c11/n1570.html#7.1.1) for the C library: "A string is a contiguous sequence of characters terminated by and including the first null character. … The length of a string is the number of bytes preceding the null character …". See also [§6.5.3.4](http://port70.net/~nsz/c/c11/n1570.html#6.5.3.4), [§6.4.5](http://port70.net/~nsz/c/c11/n1570.html#6.4.5) and [§7.24.6.3](http://port70.net/~nsz/c/c11/n1570.html#7.24.6.3). — Jonathan Leffler, Oct 01 '21 at 14:17
@user786 What is the problem to read the description of the function?! — Vlad from Moscow, Oct 01 '21 at 14:19
@Gerhardh no different result. its working as the assumption — user786, Oct 01 '21 at 14:26
@VladfromMoscow I have a function like this `void tm(char ***path)` can u please tell how to change second character of string that I am getting in `tm(char ***path)` function from some other function? — user786, Oct 01 '21 at 14:29
@user786 If you have a parameter `char ***path` you are almost certainly doing something wrong. (There is a term "[three star programmer](http://wiki.c2.com/?ThreeStarProgrammer)" and it is not a compliment! :-) ) — Steve Summit, Oct 01 '21 at 14:31
@SteveSummit I didn't do it but I think I should know how to do it — user786, Oct 01 '21 at 14:36
@VladfromMoscow I have asked a question can u please look https://stackoverflow.com/questions/69407760/threee-indirection-pointer-how-to-change-indirected-strings-index-character — user786, Oct 01 '21 at 14:40
@user786 and please don't post another unrelated question in a comment, but post an all new question. You have >2000 of reputation, you should know that. — Jabberwocky, Oct 01 '21 at 15:12

score 1 · Accepted Answer · answered Oct 01 '21 at 14:42

1

Yes that is what you would expect. Just be cautious if you were tempted to use sizeof rather than strlen on the array:

char *null_terminated_array="hello";
char char_array[6]="hello";    

printf("null_terminated_array = %s\n",null_terminated_array);
printf("strlen(null_terminated_array) = %zu\n",strlen(null_terminated_array));
printf("sizeof(null_terminated_array) = %zu\n",sizeof(null_terminated_array));
printf("\n");
printf("char_array = %s\n",char_array);
printf("strlen(char_array) = %zu\n",strlen(char_array));
printf("sizeof(char_array) = %zu\n",sizeof(char_array));

for the platform that I ran this on this gives

null_terminated_array = hello
strlen(null_terminated_array) = 5
sizeof(null_terminated_array) = 8

char_array = hello
strlen(char_array) = 5
sizeof(char_array) = 6

The apparent discrepancy for sizeof(null_terminated_array) is to do with automatic memory allocation using blocks of 32bits (platform dependent).

answered Oct 01 '21 at 14:42

ChrisBD

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can u please tell `sizeof()` does it check for null termination or not if argument in char pointer or it does not check for null termination. I am thinking if it does not check for null termination in string argument then how can sizeof an object can be found? Is there a thing that I am missing completely can u tell more – user786 Oct 01 '21 at 15:18
Sizeof does not "check" anything. The compiler tries to work out the amount of memory that the variable or type takes. If it's a `char[10]` it will be replaced by `10`. If it's something like a `char[]` or `char *` that points to a string literal, it will be replaced by the length of the string literal AND the trailing `\0`. This will only be true if the string literal is in the same scope (function or global). As e.g. a function argument it would only get the size of a pointer, because the compiler can't assume from which scope and with which arguments the function is called. – Cheatah Oct 01 '21 at 22:13

strlen(null_terminated_array) does printf("%zu", strlen(null_terminated_array)) prints size_t that includes '\0'

1 Answers1