php内置函数分析之str_pad()

 1 PHP_FUNCTION(str_pad) 2 { 3 ????/* Input arguments */ 4 ????zend_string *input; ???????????????/* Input string 输入字符串*/ 5 ????zend_long pad_length; ???????????/* Length to pad to 填充到多长.*/ 6 ?7 ????/* Helper variables */ 8 ????size_t num_pad_chars; ???????/* Number of padding characters (total - input size) 要填充进去的字符个数*/ 9 ????char *pad_str = " "; /* Pointer to padding string */10 ????size_t pad_str_len = 1; // 填充字符的个数 11 ????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*/12 ????size_t ??????i, left_pad=0, right_pad=0;13 ????zend_string *result = NULL; ???/* Resulting string 返回值*/14 15 ????if (zend_parse_parameters(ZEND_NUM_ARGS(), "Sl|sl", &input, &pad_length, &pad_str, &pad_str_len, &pad_type_val) == FAILURE) {16 ????????return;17 ????}18 19 ????/* If resulting string turns out to be shorter than input string,20 ???????we simply copy the input and return. */21 ????/* 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。*/22 ????if (pad_length < 0 ?|| (size_t)pad_length <= ZSTR_LEN(input)) {23 ????????RETURN_STRINGL(ZSTR_VAL(input), ZSTR_LEN(input));24 ????}25 26 ????/* 填充字符串长度为0，如：str_pad("abc", 10, "")，则Warning级别的错误。27 ???????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。*/28 ????if (pad_str_len == 0) {29 ????????php_error_docref(NULL, E_WARNING, "Padding string cannot be empty");30 ????????return;31 ????}32 33 ????/*pad_type只能为STR_PAD_LEFT, STR_PAD_RIGHT, or STR_PAD_BOTH 或 0, 1, 2*/34 ????if (pad_type_val < STR_PAD_LEFT || pad_type_val > STR_PAD_BOTH) {35 ????????php_error_docref(NULL, E_WARNING, "Padding type has to be STR_PAD_LEFT, STR_PAD_RIGHT, or STR_PAD_BOTH");36 ????????return;37 ????}38 39 ????num_pad_chars = pad_length - ZSTR_LEN(input); // 需要被填充进去的字符的数量40 ????if (num_pad_chars >= INT_MAX) { // num_pad_chars的最大值是2147483647。#define INT_MAX 214748364741 ????????php_error_docref(NULL, E_WARNING, "Padding length is too long");42 ????????return;43 ????}44 45 ????result = zend_string_safe_alloc(1, ZSTR_LEN(input), num_pad_chars, 0);46 ????ZSTR_LEN(result) = 0;47 48 ????/* We need to figure out the left/right padding lengths. */49 ????switch (pad_type_val) {50 ????????case STR_PAD_RIGHT:51 ????????????left_pad = 0;52 ????????????right_pad = num_pad_chars;53 ????????????break;54 55 ????????case STR_PAD_LEFT:56 ????????????left_pad = num_pad_chars;57 ????????????right_pad = 0;58 ????????????break;59 60 ????????// 左填充数量小于右，left_pad <= right_pad61 ????????case STR_PAD_BOTH:62 ????????????left_pad = num_pad_chars / 2;63 ????????????right_pad = num_pad_chars - left_pad;64 ????????????break;65 ????}66 67 ????/* First we pad on the left. */68 ????/* 左填充：循环添加字符 */69 ????for (i = 0; i < left_pad; i++)70 ????????ZSTR_VAL(result)[ZSTR_LEN(result)++] = pad_str[i % pad_str_len];71 72 ????/* Then we copy the input string. */73 ????/* 左填充完成后，附加输入字符串 */74 ????memcpy(ZSTR_VAL(result) + ZSTR_LEN(result), ZSTR_VAL(input), ZSTR_LEN(input));75 ????ZSTR_LEN(result) += ZSTR_LEN(input);76 77 ????/* Finally, we pad on the right. */78 ????/* 右填充：循环添加字符串 */79 ????for (i = 0; i < right_pad; i++)80 ????????ZSTR_VAL(result)[ZSTR_LEN(result)++] = pad_str[i % pad_str_len];81 82 ????// 添加字符串结束标志‘\0‘83 ????ZSTR_VAL(result)[ZSTR_LEN(result)] = ‘\0‘;84 85 ????// 返回新字符串86 ????RETURN_NEW_STR(result);87 }