Calculating length of a string in C

Question

int strlength(const char *myStr){
    //variable used for str length counter
    int strlength = 0;
    //loop through string until end is reached. Each iteration adds one to the string length
        while (myStr[strlength] != '\0'){
            putchar(myStr[strlength]);
            strlength++;
        }

    return strlength;
}

Why will this not work as intended? I just want to find the length of a string.

Duplicate of [C size char* array](http://stackoverflow.com/questions/1559925/c-sizeof-char-array) — Kyle, Jan 26 '13 at 19:31
If you're getting 6 instead of 5, you might do better printing `printf(" %d", mySte[strlength]);` so you can see exactly what's being processed. But the code should produce 5 for "hello". Are you sure you're testing what is written in the question? — Jonathan Leffler, Jan 26 '13 at 19:33
@Joe but if the string is hello. then myStr[5] should not allow the loop to execute right? So then the value should be correct — SystemFun, Jan 26 '13 at 19:34
@DanielFischer how so? It's the same question. How do I find the size of an array. — Kyle, Jan 26 '13 at 19:35
@KyleRogers He is not trying to get the size of the array, but the lengh of his string, which is similar in MOST platforms, but not everywhere. — Kevin, Jan 26 '13 at 19:37

score 4 · Accepted Answer · answered Jan 26 '13 at 19:35

4

From a comment on another answer:

I am using fgets to read in a string. and i have checked to make sure that the string that was typed was stored correclty

In that case, there is a trailing newline stored, so your function computes

strlength("hello\n")

The code is correct, you just didn't pass it the input you believed to pass.

answered Jan 26 '13 at 19:35

Daniel Fischer

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What do you want to avoid exactly? If you don't want a `\n` at the end of the string, just remove it. (Or, if `fgets` doesn't do what you want, don't use it.) – David Schwartz Jan 26 '13 at 19:40
@Vlad If you have POSIX, you can use `getline()`. Otherwise, compute the length, and overwrite the newline [if there is one, if the input was longer than the size passed to `fgets`, there won't be one]. – Daniel Fischer Jan 26 '13 at 19:41
@David. I'm unsure I understand fgets properlyy then. Will it always store a '\n'? – SystemFun Jan 26 '13 at 19:42
@Vlad: No. It will only store a newline in the string if it reads a newline. "`fgets()` reads in at most one less than `size` characters from `stream` and stores them into the buffer pointed to by `s`. Reading stops after an `EOF` or a newline. If a newline is read, it is stored into the buffer. A `\0` is stored after the last character in the buffer." – David Schwartz Jan 26 '13 at 19:44
@David. Well then it will always store a '\n' Unless you hit enter after the maximum length specified is reached correct? – SystemFun Jan 26 '13 at 19:48
@Vlad If there is a newline in the input stream, `fgets` will store it if there is space in the buffer (according to the size argument). – Daniel Fischer Jan 26 '13 at 19:48
@Vlad: Consider a file that only contains the letter "A". Reading stops at end of file. – David Schwartz Jan 26 '13 at 19:49
Ok thanks. I think I understand. Is there a better option than fgets() if getline() is not avilable? – SystemFun Jan 26 '13 at 19:51
@Vlad Depends on what "better" means. You could also `scanf("%99s", myStr);` [assuming `myStr` has space for 100 `char`s], that will leave the newline in the input buffer and not store it. You can also write your own input function repeatedly calling `getchar()`. – Daniel Fischer Jan 26 '13 at 19:54

score 3 · Answer 2 · answered Jan 26 '13 at 19:30

3

More reliable version:

size_t strlength(const char * myStr)
{
    return strlen(myStr);
}

answered Jan 26 '13 at 19:30

James M

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1

I think this kinda defeats the purpose of the OP's function though :P. still +1 for mentioning the conventional way. – Kevin Jan 26 '13 at 19:34
It's not homework. At all. I can easily fix it by subtracting 1 from my return. but i shouldn't need to and I dont know why – SystemFun Jan 26 '13 at 19:37

score 2 · Answer 3 · answered Jan 26 '13 at 19:29

2

You can try this also:-

int string_length(char *s)
{
   int c = 0;

   while(*(s+c))
      c++;

   return c;
}

answered Jan 26 '13 at 19:29

Rahul Tripathi

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Please explain the concept/concepts behind this. – Deepeshkumar Oct 17 '15 at 16:50
Got it when the *(s+c) expression returns 0 as it encounters a null terminating character.. The loop stops! right? Incredible! – Deepeshkumar Oct 17 '15 at 17:03

askmish · Answer 4 · 2013-01-26T19:48:35.157

No need to worry about fgets() and removing the trailing \n.

while (myStr[strlength] != '\0'){
            putchar(myStr[strlength]);
            strlength++; //When mysStr[strlength] == \0, this line would have already incremented by 1
}

Quick fix:

return (strlength-1);//This will return correct value.

A more better approach:

int strlen(const char *s)
{
   char *str=s;
   while(*str)
   {
      str++;
   }
   return (s-str);
}

Calculating length of a string in C

4 Answers4