谁能帮我详细解答一下C++中atoi的使用条件？

[LCR189]

代码如下：

#include <iostream>
#include <string>
#include <vector>
using namespace std;

class BoulderRace
{
public:
int winner(vector <string> boulders, int distance);
};

int BoulderRace::winner(vector <string> boulders, int distance)
{
vector <int>count;
int min, locat;
for( int i = 0; i < boulders.size(); i++ )
{
int time = 0, k = 0, m = 0, Dis = 0;
for( int j = 0; j < boulders[i].length(); j++ )
Dis = Dis + atoi( boulders[i][j] ); //此处atoi达不到效果。
k = distance / Dis;
time = k * boulders[i].length();
Dis = Dis * k;
while( Dis < distance )
{
Dis = Dis + boulders[i][m];
time++;
m++;
}
count.push_back( time );
}
min = count[0];
locat = 0;
for( int n = 1; n < count.size(); n++ )
{
if( count[n] < min )
{
min = count[n];
locat = n;
}
}
return locat;
}

[duke56]

[code=C/C++]or( int j = 0; j < boulders[i].length(); j++ )
Dis = Dis + atoi( &boulders[i][j] ); //?[code]

[fjbuilding]

原因有2：
1.有可能boulders[i][j]返回的是一个浮点数如0.1234，这样由于您使用的是atoi（故名思意array to integer），atoi将只能返回0；此情况下建议使用atof（array to float），它将返回0.1234；

2.有可能boulders[i][j]虽然返回了一个整形比如1234，但是您使用了这一句：k = distance / Dis;
其中k，distance全部是int型的，这就导致如果distance=100，而Dis=1234，k将得到0；这种情况下建议您把所有需要进行精确运算的变量换成float或者double型，当然atoi也要换成atof；

详见msnd；

[LCR189]

也就是说atoi的实参只能是指针？

[LCR189]

int i=atoi( const char* );

[duke56]

[Quote=引用 3 楼 lcr189 的回复:]
也就是说atoi的实参只能是指针？
[/Quote]

是指针

int atoi( const char *string );//函数原型

[wade_2003]

int time = 0, k = 0, m = 0, Dis = 0;
for( int j = 0; j < boulders[i].length(); j++ )
Dis = Dis + atoi( boulders[i][j] ); //此处atoi达不到效果。
k = distance / Dis;

达不到效果是什么意思？

#include <stdlib.h>
#include <stdio.h>

void main( void )
{
   char *s; double x; int i; long l;

   s = "  -2309.12E-15";    /* Test of atof */
   x = atof( s );
   printf( "atof test: ASCII string: %s\tfloat:  %e\n", s, x );

   s = "7.8912654773d210";  /* Test of atof */
   x = atof( s );
   printf( "atof test: ASCII string: %s\tfloat:  %e\n", s, x );

   s = "  -9885 pigs";      /* Test of atoi */
   i = atoi( s );
   printf( "atoi test: ASCII string: %s\t\tinteger: %d\n", s, i );

   s = "98854 dollars";     /* Test of atol */
   l = atol( s );
   printf( "atol test: ASCII string: %s\t\tlong: %ld\n", s, l );
}


Output

atof test: ASCII string:   -2309.12E-15   float:  -2.309120e-012
atof test: ASCII string: 7.8912654773d210   float:  7.891265e+210
atoi test: ASCII string:   -9885 pigs      integer: -9885
atol test: ASCII string: 98854 dollars      long: 98854

[LCR189]

Dis = Dis + atoi( boulders[i][j] ); //此处atoi达不到效果

此处boulders[i][j]是 (string) boulders[i]中的一个元素。

那么请问atoi可以用于string对象吗?