strlen() in crashing .exe

Question

int main()
{
    int LengthofWord = strlen('word');
    printf("%s", LengthofWord);
}

For some reason this code is crashing. I want to retrieve the length of a string ( in this case string) to use later on. Why is this code crashing?

Thanks

@DavidHeffernan: I suppose that's interpreted by some compilers as a multibyte literal, it should be of type `int` or something like that, and gets implicitly casted to `char *`, which tragic results. — Matteo Italia, Dec 26 '13 at 18:07

David Heffernan · Answer 1 · 2013-12-26T18:17:34.260

4

You have these problems with your code:

This is not valid: 'word'. The ' symbol is used for single characters, for instance 'a'. You meant to write "word".
The type of LengthofWord should be size_t rather than int since that is what strlen returns.
You used the wrong format string for printf. You used %s which is appropriate for a string. For an integral value, you should use %zu. Although, do beware that some runtimes will not understand %zu.
Your main signature is incorrect – it should be int main(void)

So your complete program should be:

#include <stdio.h>
#include <string.h>

int main(void)
{
    size_t LengthofWord = strlen("word");
    printf("%zu", LengthofWord);
}

edited Dec 26 '13 at 18:17

answered Dec 26 '13 at 18:05

David Heffernan

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Why should it be size_t? What is the diffrence between size_t and int? – user2955782 Dec 26 '13 at 18:12
2

It should be `size_t` because that's what `strlen` returns. What's the difference between `size_t` and `int`. Well, they are just different things. At the very least, `size_t` is unsigned, and `int` is signed. And they may be different sizes. – David Heffernan Dec 26 '13 at 18:13
You can't say or rely on that `int` is `sighned` or `unsigned`. – haccks Dec 26 '13 at 18:19
1

@haccks Yes you can. int is always signed. char can be signed or unsigned, but the other basic integer types (short, int, long, long long) are always signed. – Nigel Harper Dec 26 '13 at 18:42

alk · Answer 2 · 2013-12-26T18:09:28.003

3

It should be

... = strlen("word");

In C string literals are put into double quotation marks.

Also strlen() returns size_t not int. So the full line shall look like this:

size_t LengthofWord = strlen("word");

Finally to print out a size_t use the conversion specifier "zu":

printf("%zu", LengthofWord);

A "%s" expects a 0-terminated array of char, a "string".

Last not least, start the program using

int main(void)
{
  ...

and finish it by returing an int

  ...
  return 0;
}

edited Dec 26 '13 at 18:09

answered Dec 26 '13 at 18:04

alk

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What does %zu do/mean? Also what is a size_t? – user2955782 Dec 26 '13 at 18:11
1

`return` is optional in `main`. – David Heffernan Dec 26 '13 at 18:14
Not necessary to print `size_t` with `%zu`. – haccks Dec 26 '13 at 18:14
@DavidHeffernan: Then I'd needed to limit my answer to C99 and above. – alk Dec 26 '13 at 18:16
@alk. It is allowed in C99 to omit the `return 0` statement from `main`. – haccks Dec 26 '13 at 18:17
@haccks: On machines where `size_t` has a higher rank than `int` it is necessary, 64bit machine typically. – alk Dec 26 '13 at 18:17
@alk; Yes. That's what I mean. – haccks Dec 26 '13 at 18:18
@user2955782: `size_t` is an unsigned integer type guaranteed to be able to hold the maximum possible size of an object that can be created on the machine the code is compiled for. `zu` is the conversion specfier `u` for unsigned, prefixed by the length modifer for `size_t`/`ssize_t` which is `z`. – alk Dec 26 '13 at 18:38

score 2 · Answer 3 · edited May 23 '17 at 12:11

There is difference between ' quote and " quote in C. For strings " is used.
Change

int LengthofWord = strlen('word');  
                          ^    ^
                          |    |
                          -----------Replace these single quotes with double quotes("")

to

int LengthofWord = strlen("word");

strlen returns size_t type. Declare it as size_t type instead of int. Also change the format specifier in the printf to %zu

  printf("%d", LengthofWord);

Your final code should look like

int main(void)
{
    size_t LengthofWord = strlen('word');
    printf("%zu", LengthofWord);

    return 0;
}

strlen() in crashing .exe

3 Answers3