C++ 读取字符串中的数字

// 方法1：一个字符一个字符读取
#include <iostream>
#include <string>
#include <fstream>
#include <stdlib.h>
using namespace std;
int main()
{
    ifstream fin("data.txt");
    if(! fin.is_open())
    {
        cout<<"Error opening file"<<endl;exit(1);
    }
    char str;
    int num[10001];
    int i=0;num[i] = 0;
    bool IsNegative = false;
    while(!fin.eof()){
        fin.read(&str,1);
        if(str == ‘ ‘){
            if(IsNegative) num[i] = -num[i];
            printf("%d ",num[i]);
            i += 1;num[i] = 0;
            IsNegative = false;
        }
        else if(str == ‘\0‘ || str == ‘\n‘){
            if(IsNegative) num[i] = -num[i];
            printf("%d ",num[i]);
            i += 1;num[i] = 0;
            break;
        }
        else if(str == ‘-‘){
            IsNegative = true;
        }
        else{
            num[i] = num[i]*10 + (str-‘0‘);
        }
    }    
    return 0;
}

//方法2：借助strtok实现split 适用于char
#include <iostream>
#include <string>
#include <fstream>
#include <string.h>
#include <stdio.h>
using namespace std;
int ReadNum(char *str){
    int i = 0;
    int num = 0;
    if(str[0] == ‘-‘){
        i += 1;
    }
    while(str[i]){
        num = (str[i]-‘0‘) + num*10;
        i += 1; 
    }
    if(str[0] == ‘-‘){
        num = -num;
    }
    return num;
}

int main()
{
    ifstream fin("data.txt");
    if(! fin.is_open())
    {
        cout<<"Error opening file"<<endl;exit(1);
    }
    char s[10001];
    int num[101];int i = 0;
    fin.getline(s,10001);
    const char *d = " ";
    char *p;
    p = strtok(s,d);
    while(p)
    {
            num[i] = ReadNum(p);
            printf("%d ",num[i]);
            i+=1;
            p=strtok(NULL,d);
    }
    return 0;
}

//方法3：借助istringstream实现split 适用于string 
#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
using namespace std ;
int ReadNum(string str){
    int i = 0;
    int num = 0;
    if(str[0] == ‘-‘){
        i += 1;
    }
    while(str[i]){
        num = (str[i]-‘0‘) + num*10;
        i += 1; 
    }
    if(str[0] == ‘-‘){
        num = -num;
    }
    return num;
}
int main(){
    ifstream fin("data.txt");
    if(! fin.is_open())
    {
        cout<<"Error opening file"<<endl;exit(1);
    }
    string str;
    getline(fin, str);
    string sTmp;
    istringstream istr(str);
    int num[100000];int i = 0;
    while(!istr.eof()){
        istr >> sTmp; //get a word
        num[i] = ReadNum(sTmp);
        printf("%d ", num[i]);
        i += 1;
    }
    return 0;
}