声明char 类型的NULL指针,在输出指针变量的值之后,程序就像是终止了一样,导致后面的判断语句不执行了。请大神指点下。
相关代码:
#include<iostream>
#include<string>
using namespace std;
int main() {
// int *var = NULL;
// short *var = NULL;
// long *var = NULL;
// float *var = NULL;
// double *var = NULL;
// bool *var = NULL;
char *var = NULL;
// string *var = NULL;
cout << "var's value is " << var << endl;
// 很奇怪的现象是:
// 当指针类型为 char 时, 下面的判断语句不执行了!
if(var) {
cout << "var is not null pointer." << endl;
} else {
cout << "var is null pointer." << endl;
}
}
期望在控制套输出的结果是:
var's value is 0
var is null pointer.
实际在控制台输出的结果是:
var's value is 0
补充说明:
1. 使用 g++ 编译的时候并未提示错误。
2. 将指针类型修改为 int 或者 string 的时候,均可得到期望的结果。
3. 使用 VS 调试这段代码的时候,弹出了 Visual Studio 2019 已经停止了工作 的提示
#include<iostream>
#include<string>
using namespace std;
int main() {
char* var = NULL;
cout << "var's value is " << (int)var << endl;
if (var) {
cout << "var is not null pointer." << endl;
}
else {
cout << "var is null pointer." << endl;
}
}
你可以尝试一下这样写
const char* var = "123";
cout << "var's value is " << var << endl;
cout << "var's value is " << "123"<< endl;
cout 把char * 理解成了指向字符串的指针了把
希望这个可以帮到你
#include<iostream>
#include<string>
using namespace std;
int a;
char b;
float c;
double d;
bool boo;
string str;
int *e;
char *f;
float *g;
double *h;
string *s;
int main() {
cout<<"int "<<a<<endl<<"char "<<b<<endl<<"float "<<c<<endl<<"double "<<d<<endl<<"string "<<str<<endl<<"bool "<<boo<<endl;
cout<<"int* "<<e<<endl<<"float* "<<g<<endl<<"double* "<<h<<endl<<"string* "<<s<<endl<<"char* "<<f<<endl;
return 0;
}