?? ?float a = 1122.334455;
?? ?std::stringstream buf;
?? ?buf.precision(2);//覆蓋默認(rèn)精度
?? ?buf.setf(std::ios::fixed);//保留小數(shù)位
?? ?buf << a << "文字";
?? ?std::string str;
?? ?str = buf.str();

? ? float a = 1122.334455;
?? ?char* chCode;
?? ?chCode = new(std::nothrow)char[20];
?? ?sprintf(chCode, "%.2lf", a);// .2 是控制輸出精度bai的，兩位小數(shù)
?? ?std::string strCode(chCode);
?? ?delete []chCode;

#include <iostream>
#include <string>
#include <string.h>
#include <stdlib.h>

using namespace std;

int main(int argc, char *argv[]) {
?? ?const string tmp_str = "0.1285354";
?? ?float tmp_f = 0;
?? ?double tmp = 0;
?? ?cout.precision(16);
?? ?cout << sizeof(tmp_f) << "--" << sizeof(tmp) << endl;
?? ?cout << stof(tmp_str) << endl;
?? ?cout << stod(tmp_str) << endl;
?? ?cout << stold(tmp_str) << endl;
?? ?cout << strtod(tmp_str.c_str(), NULL) << endl;
?? ?cout << atof(tmp_str.c_str()) << endl;
?? ?tmp = 0.1234567890123456;
?? ?cout << tmp << endl;
?? ?return 0;
}

#include <iostream>
double tmp = 0.1234567890123456;
cout.precision(16);?? ?//此處設(shè)置后，全局有效；cout浮點(diǎn)數(shù)輸出精度均為16
cout << tmp << endl;

#include <iostream>
#include <iomanip>
double tmp = 0.1234567890123456;
cout << setprecision(16) << tmp << endl; //此處設(shè)置后，全局有效；后面cout浮點(diǎn)數(shù)輸出精度均為16
cout << 0.1234567890123456 << endl;?? ?// 0.1234567890123456