How Long Is a String?
Sometimes, you need to know how many bytes are taken by a string. In C, you can use a function called strlen() to measure the length of a string.
The strlen() Function
Let's have a look at the syntax of the strlen() function.
The syntax for the strlen() function is
#include <string.h>
size_t strlen(const char *s);
Here s is a char pointer variable. The return value from the function is the number of bytes. size_t is a data type defined in the string.h header file. The size of the data type depends on the particular computer system. Note that string.h has to be included in your program before you can call the strlen() function.
Listing 13.2 gives an example of using the strlen() function to measure string lengths.
TYPE
Listing 13.2. Measuring string lengths.1: /* 13L02.c: Measuring string length */
2: #include <stdio.h>
3: #include <string.h>
4:
5: main()
6: {
7: char str1[] = {`A', ` `,
8: `s', `t', `r', `i', `n', `g', ` `,
9: `c', `o', `n', `s', `t', `a', `n', `t', `\0'};
10: char str2[] = "Another string constant";
11: char *ptr_str = "Assign a string to a pointer.";
12:
13: printf("The length of str1 is: %d bytes\n", strlen(str1));
14: printf("The length of str2 is: %d bytes\n", strlen(str2));
15: printf("The length of the string assigned to ptr_str is: %d bytes\n",
16: strlen(ptr_str));
17: return 0;
18: }
OUTPUT
I get the following output by running the executable 13L02.exe of the program in Listing 13.2 from a DOS prompt:
ANALYSIS
C:\app>13L02
The length of str1 is: 17 bytes
The length of str2 is: 23 bytes
The length of the string assigned to ptr_str is: 29 bytes
C:\app>
In Listing 13.2, two char arrays, str1 and str2, and one pointer variable, ptr_str, are declared and initialized in lines 7_11, respectively.
Then, the statement in line 13 obtains the length of the string constant held by str1, and prints out the result on the screen. From the result, you can see that the null character (\0) contained by the last element of str1 is not counted by the strlen() function.
In lines 14_16, the lengths of the string constants referenced by str2 and ptr_str are measured and shown on the screen. The results indicate that the strlen() function does not count the null characters appended to the two string constants by the compiler, either.
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