字符串转为整数，不考虑进制

// 字符串转换为整数，字符串可能包含：// 1.开头和结尾可能有空格，// 2.可能有+-号// 3.可能有非法符号，这时结束转换// 4.可能溢出，这时返回0#include <iostream>   #include <assert.h>#include <string.h>using namespace std;  int str2Int(const char *str){assert(str!= NULL);int n=strlen(str);const char *p1=str, *p2=str+n-1;// dealing with spacewhile (isspace(*p1) && p1<=p2){p1++;}while (isspace(*p2) && p1<=p2){p2--;}//int nSymbol=1;if (p1[0]=='+'){nSymbol=1;p1++;}else if (p1[0]=='-'){nSymbol=-1;p1++;}else if (!isdigit(p1[0])){return 0;}int sum=0;while (p1<=p2){if (!isdigit(p1[0])){return sum*nSymbol;}sum = sum*10 + (unsigned char)(*p1 - '0');if(sum<0){cout<<"溢出!"<<endl;return 0;}p1++;}return sum*nSymbol;}int main(){char str1[]="99999999999999999999999300";char str2[]="-35.9  ";char str3[]="p300";char str4[]=" 34d0 t";cout<<str1<<" str2Int(): "<<str2Int(str1)<<"    atoi:  "<<atoi(str1)<<endl;cout<<str2<<" str2Int(): "<<str2Int(str2)<<"    atoi:  "<<atoi(str2)<<endl;cout<<str3<<" str2Int(): "<<str2Int(str3)<<"    atoi:  "<<atoi(str3)<<endl;cout<<str4<<" str2Int(): "<<str2Int(str4)<<"    atoi:  "<<atoi(str4)<<endl;return 0;}