Distinct Outputs in String Length and Size Calculations for Pointer-Based and Array-Based String Initialization

Understanding the Results

When creating a pointer-based string str1 and an array-based string str2 with the same value, the functions strlen and sizeof produce different results. Specifically, for the declarations:

char *str1 = "Sanjeev";
char str2[] = "Sanjeev";

strlen returns 7 for both str1 and str2 since it measures the length of the character sequence, excluding the null-terminator (\0) at the end.

However, sizeof yields different values:

• sizeof(str1) returns 4 because it evaluates the size of the pointer variable, which is typically 4 bytes (32-bit systems).
• sizeof(str2) returns 8 because it determines the size of the array, which includes the null-terminator, resulting in 8 bytes (7 characters 1 null-terminator).

The Underlying Difference: Data Type versus Memory Allocation

sizeof measures the size of the data type, while strlen measures the length of the character sequence. In the case of str1, it is a pointer to a char, so sizeof returns the size of the pointer. For str2, it is an array of chars, so sizeof returns the size of the entire array, including the null-terminator.

A Closer Look

To demonstrate the distinction better, consider:

char str2[8];
strncpy(str2, "Sanjeev", 7);
char *str1 = str2;

Now, both str1 and str2 point to the same array. Their strlen values are 7, but their sizeof values differ:

• sizeof(str1) is 4 (pointer size)
• sizeof(str2) is 8 (array size with null-terminator)

This exemplifies how the size evaluation depends on the underlying data structure.