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

Question

Puneet Kankar · Answer

sizeof() Sizeof operator is a compile time unary operator which can be used to compute the size of its operand. The result of sizeof is of unsigned integral type which is usually denoted by size_t. sizeof can be applied to any data-type, including primitive types such as integer and floating-point types, pointer types, or compound datatypes such as Structure, union etc. strlen() strlen() is a predefined function in C whose definition is contained in the header file “string.h”. strlen() accepts a pointer to an array as argument and walks through memory at run time from the address we give it looking for a NULL character and counts up how many memory locations it passed before it finds one. The main task of strlen() is to count the length of an array or string. sizeof vs strlen() Type: Sizeof operator is a unary operator whereas strlen() is a predefined function in C 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. 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. Summary: The two are almost different concepts and used for different purposes. 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) .

Madan Shekar · Answer

strlen() searches for that NULL character and counts the number of memory address passed, So it actually counts the number of elements present in the string before the NULL character, here which is 8. sizeof() operator returns actual amount of memory allocated for the operand passed to it. Here the operand is an array of characters which contains 9 characters including Null character and size of 1 character is 1 byte. So, here the total size is 9 bytes. #include #include using namespace std; int main() { char a[] = { "Geeks for" }; char b[] = { 'G' , 'e' , 'e' , 'k' , 's' , ' ' , 'f' , 'o' , 'r' }; cout "sizeof(a) = " sizeof (a); cout "
strlen(a) = " strlen (a); cout "
sizeof(b) = " sizeof (b); cout "
strlen(b) = " strlen (b); return 0; } sizeof vs strlen() Type: Sizeof operator is a unary operator whereas strlen() is a predefined function in C 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. 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. Summary: The two are almost different concepts and used for different purposes. 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) .

Sanwar Ranwa · Answer

Hello 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
" , 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
" , sizeof ( a )); printf ( "Size of int data type : %d
" , sizeof ( int )); printf ( "Size of char data type : %d
" , sizeof ( char )); printf ( "Size of float data type : %d
" , sizeof ( float )); printf ( "Size of double data type : %d
" , 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 For more Details please check these Links https://www.geeksforgeeks.org/difference-strlen-sizeof-string-c-reviewed/ https://www.studytonight.com/c/programs/string/difference-between-strlen()-and-sizeof()-function https://www.tutorialspoint.com/difference-between-strlen-and-sizeof-for-string-in-c

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

Answers (3)