How to convert php string to integer

How to convert php string to integer type: 1. Use the "intval($num);" method to convert the string type number into an integer type number; 2. Use the ascii code to convert the string type into an integer type number. Convert to integer type.

The operating environment of this article: Windows7 system, PHP7.1 version, DELL G3 computer

PHP-String to integer- Do not use built-in functions

Introduction

If you want to convert php string type numbers into integer numbers, generally we use the system’s built-in API to do the conversion, but if What should we do if the regulations do not allow us to use the system's built-in API conversion, but allow us to implement a function conversion ourselves? Here we look at how to achieve it.

System built-in API method

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

Use ASCII code method

Next we use ascii code method to do the conversion, Because each character corresponds to an ASCII code, when adding, subtracting, multiplying, and dividing this character, it is actually adding, subtracting, multiplying, and dividing the ASCII code, that is, an integer operation, which will eventually return an integer number.

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The ASCII codes of characters '0' ~ '9' are 48~57. When converting, we subtract each character '0' For example: '1' - '0' = 1, '2' - '0' = 2 The return value is an Int type, see the code implementation below.

function convertInt($strInt = ''){ 
    $len = strlen($strInt);  
    $int = 0;
 
    for($i=0;$i<$len;$i++){
        $int *= 10;            
        $num = $strInt{$i} - &#39;0&#39;;            
        $int += $num;        
    }
 
    return $int;        
}
 
 $num = &#39;345432123&#39;;    
 var_dump(convertInt($num)); //输出： int(345432123)
在 Redis 里面也有提供一个字符串转整型的函数，也是通过ascii码方式去做的，实现的比较完善严谨，具体可以参考下
string2ll 函数
#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] == &#39;0&#39;) {
        if (value != NULL) *value = 0;
        return 1;
    }
 
    if (p[0] == &#39;-&#39;) {
        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] >= &#39;1&#39; && p[0] <= &#39;9&#39;) {
        v = p[0]-&#39;0&#39;;
        p++; plen++;
    } else if (p[0] == &#39;0&#39; && slen == 1) {
        *value = 0;
        return 1;
    } else {
        return 0;
    }
 
    while (plen < slen && p[0] >= &#39;0&#39; && p[0] <= &#39;9&#39;) {
        if (v > (ULLONG_MAX / 10)) /* Overflow. */
            return 0;
        v *= 10;
 
        if (v > (ULLONG_MAX - (p[0]-&#39;0&#39;))) /* Overflow. */
            return 0;
        v += p[0]-&#39;0&#39;;
 
        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;
}

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