PHP不使用内置函数实现字符串转整型的方法示例

$num = '345432123'; //（一）$num = (int)$num;//输出：//int(345432123)//（二）$num = intval($num);//输出：//int(345432123)

function convertInt($strInt = ''){  $len = strlen($strInt);  $int = 0; for($i=0;$i<$len;$i++){  $int *= 10;     $num = $strInt{$i} - '0';     $int += $num;   } return $int;  } $num = '345432123';  var_dump(convertInt($num)); //输出： int(345432123)

#include <stdio.h>#include <limits.h>#include <string.h>/* Convert a string into a long long. Returns 1 if the string could be parsed * into a (non-overflowing) long long, 0 otherwise. The value will be set to * the parsed value when appropriate. */int string2ll(const char *s, size_t slen, long long *value) { const char *p = s; size_t plen = 0; int negative = 0; unsigned long long v; if (plen == slen)  return 0; /* Special case: first and only digit is 0. */ if (slen == 1 && p[0] == '0') {  if (value != NULL) *value = 0;  return 1; } if (p[0] == '-') {  negative = 1;  p++; plen++;  /* Abort on only a negative sign. */  if (plen == slen)   return 0; } /* First digit should be 1-9, otherwise the string should just be 0. */ if (p[0] >= '1' && p[0] <= '9') {  v = p[0]-'0';  p++; plen++; } else if (p[0] == '0' && slen == 1) {  *value = 0;  return 1; } else {  return 0; } while (plen < slen && p[0] >= '0' && p[0] <= '9') {  if (v > (ULLONG_MAX / 10)) /* Overflow. */   return 0;  v *= 10;  if (v > (ULLONG_MAX - (p[0]-'0'))) /* Overflow. */   return 0;  v += p[0]-'0';  p++; plen++; } /* Return if not all bytes were used. */ if (plen < slen)  return 0; if (negative) {  if (v > ((unsigned long long)(-(LLONG_MIN+1))+1)) /* Overflow. */   return 0;  if (value != NULL) *value = -v; } else {  if (v > LLONG_MAX) /* Overflow. */   return 0;  if (value != NULL) *value = v; } return 1;}//-------- 执行 ---------int main(){ long long num; string2ll("345432123",strlen("345432123"),&num); printf("%d/n",num); //输出 345432123 retunr 0;}