C++中怎么把字符串string型的数字转换成整型int型的数字？

int str2int( string str) { int i,len = str.size(),num = 0 ; i = 0 ; if (str[ 0 ] == ' - ' ) i = 1 ; while (i 0 ? num : - 1 * num; while (num_) { str = ( char )(num_ % 10 + 48 ) + str;num_ /= 10 ; }