Briefly talk about the strlen function in PHP

strlen function description.

int strlen (string $string)

In this article, we can know that the strlen function is defined through Zend Engine. The function definition can be viewed here.

The source code of the function is also given here:

ZEND_FUNCTION(strlen)
{
  char *s1;
  int s1_len;
 
  if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &s1, &s1_len) == FAILURE) {
    return;
  }
 
  RETVAL_LONG(s1_len);
}

The article mentioned that the function is very simple and does not require further explanation. This article also introduces the zend_parse_parameters function. The author is stupid, so I want to understand how the zend_parse_parameters function returns the variable length.

In the zend_parse_arg_impl function, where parameters are parsed, we continue to look at the case 's' branch. This branch is the parsing of string variables.

int *pl = va_arg(*va, int *); is the definition of string length variable.

Continuing to look down, you can see the assignment statement to the pl variable: *pl = Z_STRLEN_PP(arg);.

The Z_STRLEN_PP macro is defined in the zend_operators.h file:

#define Z_STRLEN_PP(zval_pp) Z_STRLEN(**zval_pp)

Let’s continue looking at the Z_STRLEN macro Definition, #define Z_STRLEN(zval) (zval).value.str.len. From this we can know that the strlen function is implemented by directly returning the len attribute of str in the zval structure.

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