strlen in C

Purpose of strlen()

strlen() is one of the inbuilt string function in c programming which is used to find the length of the given string.

How strlen() Works

The following diagram clearly illustrate the working principle of strlen() inbuilt string function in c.

In the above diagram, strlen() will increment the count consecutively only when the next character is not '\0'.

Syntax - strlen()

• strlen() accept only one string as a parameter
• strlen() return a length of a string which is of integer type.
• To use strlen() inbuilt string functions in C, we need to declare #include<string.h> header file.

strlen(str1);

C Program - strlen()

Let us work through strlen() function, In the following program we will find the length of the string "ThisisStrlen" using strlen() inbuilt string function.

#include <stdio.h>
#include<string.h>
int main()
{
char str1[] = "ThisisStrlen";
printf("Length of str1 = %d ", strlen(str1));
return 0;
}

Length of str1 = 12

C Program - Without strlen()

Let us count the length of the string without using inbuilt string function strlen().

#include <stdio.h>
#include<string.h>
int main()
{
char str1[] = "ThisisStrlen",i;
for(i=0; str1[i]!='\0';i++)
{
//	making using i to count str1 length
}
printf("Length of str1 = %d ",i);
return 0;
}

Length of str1 = 12

Did You Know?

When a string containing '\0' in its middle i.e) This\0willbreak, then strlen() will break and return the count upto '\0' i.e) it returns 4.

#include <stdio.h>
#include<string.h>
int main()
{
char str1[] = "This\0willbreak";
printf("Length of str1 = %d ", strlen(str1));
return 0;
}

Length of str1 = 4

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