Difference between strlen() and sizeof() for string in C ?

sizeof vs strlen()

1. Type: Sizeof operator is a unary operator whereas strlen() is a predefined function in C
2. Data types supported: Sizeof gives actual size of any type of data (allocated) in bytes (including the null values) whereas get the length of an array of chars/string.
3. Evaluation size: sizeof() is a compile-time expression giving you the size of a type or a variable’s type. It doesn’t care about the value of the variable.
   Strlen on the other hand, gives you the length of a C-style NULL-terminated string.
4. Summary: The two are almost different concepts and used for different purposes.
5. In context of C++: In C++, you do not need any of them as such.
   strlen() in C-style strings can be replaced by C++ std::strings.
   sizeof() in C is as an argument to functions like malloc(), memcpy() or memset() can be replaced by C++ (use new, std::copy(), and std::fill() or constructors).

strlen()

The function strlen() is a predefined function in C language. This is declared in “string.h” header file. It is used to get the length of array or string.

Here is the syntax of strlen() in C language,

size_t strlen(const char *string);

Here,

string − The string whose length is to be calculated.

Here is an example of strlen() in C language,

Example

Live Demo

#include #include int main () {

char s1[10] = "Hello";

int len ;

len = strlen(s1);

printf("Length of string s1 : %d\n", len );

return 0;}

Output

Length of string s1 : 10

In the above example, a char type array s1 is initialized with a string and a variable len is stroing the length of s1.

char s1[10] = "Hello";

int len ;

len = strlen(s1);

sizeof()

The function sizeof() is a unary operator in C language and used to get the size of any type of data in bytes.

Here is the syntax of sizeof() in C language,

sizeof( type );

Here,

type − Any type or data type or variable, you want to calculate the size of.

Here is an example of sizeof() in C language,

Example

Live Demo

#include int main() {

int a = 16;

printf("Size of variable a : %d\n",sizeof(a));

printf("Size of int data type : %d\n",sizeof(int));

printf("Size of char data type : %d\n",sizeof(char));

printf("Size of float data type : %d\n",sizeof(float));

printf("Size of double data type : %d\n",sizeof(double));

return 0;}

Output

Size of variable a : 4

Size of int data type : 4

Size of char data type : 1

Size of float data type : 4

Size of double data type : 8