php内置函数分析之str_pad()

PHP_FUNCTION(str_pad) { /* Input arguments */ zend_string *input; /* Input string 输入字符串*/ zend_long pad_length; /* Length to pad to 填充到多长.*/ /* Helper variables */ size_t num_pad_chars; /* Number of padding characters (total - input size) 要填充进去的字符个数*/ char *pad_str = " "; /* Pointer to padding string */ size_t pad_str_len = 1; // 填充字符的个数  zend_long pad_type_val = STR_PAD_RIGHT; /* The padding type value 填充类型，左填充、右填充、左右填充。默认右填充*/ size_t i, left_pad=0, right_pad=0; zend_string *result = NULL; /* Resulting string 返回值*/ if (zend_parse_parameters(ZEND_NUM_ARGS(), "Sl|sl", &input, &pad_length, &pad_str, &pad_str_len, &pad_type_val) == FAILURE) { return; } /* If resulting string turns out to be shorter than input string, we simply copy the input and return. */ /* 如果pad_length（参数2）小于等于输入字符串的长度，则返回原始的输入字符串。*/ if (pad_length < 0 || (size_t)pad_length <= ZSTR_LEN(input)) { RETURN_STRINGL(ZSTR_VAL(input), ZSTR_LEN(input)); } /* 填充字符串长度为0，如：str_pad("abc", 10, "")，则Warning级别的错误。 填充字符串的默认长度为1，即str_pad("abc", 10)，的情况下pad_str_len=1。*/ if (pad_str_len == 0) { php_error_docref(NULL, E_WARNING, "Padding string cannot be empty"); return; } /*pad_type只能为STR_PAD_LEFT, STR_PAD_RIGHT, or STR_PAD_BOTH 或 0, 1, 2*/ if (pad_type_val < STR_PAD_LEFT || pad_type_val > STR_PAD_BOTH) { php_error_docref(NULL, E_WARNING, "Padding type has to be STR_PAD_LEFT, STR_PAD_RIGHT, or STR_PAD_BOTH"); return; } num_pad_chars = pad_length - ZSTR_LEN(input); // 需要被填充进去的字符的数量 if (num_pad_chars >= INT_MAX) { // num_pad_chars的最大值是2147483647。#define INT_MAX 2147483647 php_error_docref(NULL, E_WARNING, "Padding length is too long"); return; } result = zend_string_safe_alloc(1, ZSTR_LEN(input), num_pad_chars, 0); ZSTR_LEN(result) = 0; /* We need to figure out the left/right padding lengths. */ switch (pad_type_val) { case STR_PAD_RIGHT: left_pad = 0; right_pad = num_pad_chars; break; case STR_PAD_LEFT: left_pad = num_pad_chars; right_pad = 0; break; // 左填充数量小于右，left_pad <= right_pad case STR_PAD_BOTH: left_pad = num_pad_chars / 2; right_pad = num_pad_chars - left_pad; break; } /* First we pad on the left. */ /* 左填充：循环添加字符 */ for (i = 0; i < left_pad; i++) ZSTR_VAL(result)[ZSTR_LEN(result)++] = pad_str[i % pad_str_len]; /* Then we copy the input string. */ /* 左填充完成后，附加输入字符串 */ memcpy(ZSTR_VAL(result) + ZSTR_LEN(result), ZSTR_VAL(input), ZSTR_LEN(input)); ZSTR_LEN(result) += ZSTR_LEN(input); /* Finally, we pad on the right. */ /* 右填充：循环添加字符串 */ for (i = 0; i < right_pad; i++) ZSTR_VAL(result)[ZSTR_LEN(result)++] = pad_str[i % pad_str_len]; // 添加字符串结束标志'\0' ZSTR_VAL(result)[ZSTR_LEN(result)] = '\0'; // 返回新字符串  RETURN_NEW_STR(result); }