#有符号无符号数据类型溢出测试记录
今天遇到一个比较基础问题：若有符号位的数据类型溢出会发生什么后果？ 以前记得微机原理上说数据有原码、反码、补码3种表示形式，计算机通常的处理都是按照补码数据进行的，那么在一个数据类型的最大值溢出后会发生什么情况呢。
环境：Qt5.7
#include <QCoreApplication>
#include <limits>
#include <iostream>
#include <QString>
#include <QDebug>
#include <sys/types.h>
#define TYPE_signed int
#define TYPE_NAME_signed "int"
#define TYPE_unsigned unsigned int
#define TYPE_NAME_unsigned "unsigned int"
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
const int base = 10;
QString baseStr = base == 10 ? "" : "0x";
qDebug()<<QString(TYPE_NAME_signed" max:%1%2")
.arg(baseStr)
.arg(std::numeric_limits<TYPE_signed>::max(),0,base);
qDebug()<<QString(TYPE_NAME_signed" min:%1%2")
.arg(baseStr)
.arg(std::numeric_limits<TYPE_signed>::min(),0,base);
TYPE_signed symbTest;
symbTest = std::numeric_limits<TYPE_signed>::max();
symbTest += 1;
qDebug()<<QString(TYPE_NAME_signed" Overflow result:%1%2+1=%1%3")
.arg(baseStr)
.arg(std::numeric_limits<TYPE_signed>::max(),0,base)
.arg(symbTest,0,base);
TYPE_signed tmp = symbTest + 1;
qDebug()<<QString(TYPE_NAME_signed" Overflow result:%1%2+1=%1%3")
.arg(baseStr)
.arg(symbTest,0,base)
.arg(tmp,0,base);
qDebug()<<QString(TYPE_NAME_unsigned" max:%1%2")
.arg(baseStr)
.arg(std::numeric_limits<TYPE_unsigned>::max(),0,base);
qDebug()<<QString(TYPE_NAME_unsigned" min:%1%2")
.arg(baseStr)
.arg(std::numeric_limits<TYPE_unsigned>::min(),0,base);
TYPE_unsigned usymbText;
usymbText = std::numeric_limits<TYPE_unsigned>::max();
usymbText += 1;
qDebug()<<QString(TYPE_NAME_unsigned" Overflow result:%1%2+1=%1%3")
.arg(baseStr)
.arg(std::numeric_limits<TYPE_unsigned>::max(),0,base)
.arg(usymbText,0,base);
return a.exec();
}
分别作了几种数据类型的测试：int16_t和u_int16_t输出结果：
"int16_t max:32767" "int16_t min:-32768" "int16_t Overflow result:32767+1=-32768" "int16_t Overflow result:-32768+1=-32767" "u_int16_t max:65535" "u_int16_t min:0" "int16_t Overflow result:65535+1=0"
int和unsigned int输出结果：
"int max:2147483647" "int min:-2147483648" "int Overflow result:2147483647+1=-2147483648" "int Overflow result:-2147483648+1=-2147483647" "unsigned int max:4294967295" "unsigned int min:0" "unsigned int Overflow result:4294967295+1=0"
#结论
- 无符号位最大值加1后会变为0，重新重0开始加
- 有符号位最大值加1后会变为有符号位的最小值，继续在此基础上递增