How to get the string size in bytes

Question

As the title implies  my question is how to get the size of a string in C  Is it good to use sizeof if I ve declared it  the string  in a function without malloc in it  Or  if I ve declared it as a pointer  What if I initialized it with malloc  I would like to have an exhaustive response

User · Accepted Answer

You can use strlen  Size is determined by the terminating null-character  so passed string should be valid   If you want to get size of memory buffer  that contains your string  and you have pointer to it    If it is dynamic array created with malloc   it is impossible to get it size  since compiler doesn t know what pointer is pointing at   check this  If it is static array  you can use sizeof to get its size    If you are confused about difference between dynamic and static arrays  check this

User · Answer

While sizeof works for this specific type of string   char str      content   int charcount   sizeof str - 1     -1 to exclude terminating   0    It does not work if str is pointer  sizeof returns size of pointer  usually 4 or 8  or array with specified length  sizeof will return the byte count matching specified length  which for char type are same    Just use strlen

User · Answer

I like to use    strlen string    1     sizeof char    This will give you the buffer size in bytes  You can use this with snprintf   may help   const char  message     s  World    char  string    char  malloc  strlen message  1   sizeof char    snprintf string   strlen message  1   sizeof char   message   Hello      Cheers  Function  size t strlen  const char  s

User · Answer

If you use sizeof  then a char  str and char str   will return different answers  char str   will return the length of the string including the string terminator  while char  str will return the size of the pointer differs as per compiler

User · Answer

Use strlen to get the length of a null-terminated string   sizeof returns the length of the array not the string  If it s a pointer  char  s   not an array  char s     it won t work  since it will return the size of the pointer  usually 4 bytes on 32-bit systems   I believe an array will be passed or returned as a pointer  so you d lose the ability to use sizeof to check the size of the array   So  only if the string spans the entire array  e g  char s      stuff    would using sizeof for a statically defined array return what you want  and be faster as it wouldn t need to loop through to find the null-terminator   if the last character is a null-terminator  you will need to subtract 1   If it doesn t span the entire array  it won t return what you want   An alternative to all this is actually storing the size of the string

[c] How to get the string size in bytes?

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