C++ cerr 未定义
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时间：2020-08-28 14:28:49 来源:igfitidea点击:
cerr is undefined
提问by user195257
I have some problems, I'm getting these errors (marked in the code):
我有一些问题，我收到了这些错误（标记在代码中）：
- identifier "cerr" is undefined
- no operator "<<" matches these operands
- 标识符“cerr”未定义
- 没有运算符“<<”匹配这些操作数
Why?
为什么？
#include "basic.h"
#include <fstream>
using namespace std;
int main()
{
ofstream output("output.txt",ios::out);
if (output == NULL)
{
cerr << "File cannot be opened" << endl; // first error here
return 1;
}
output << "Opening of basic account with a 100 Pound deposit: "
<< endl;
Basic myBasic (100);
output << myBasic << endl; // second error here
}
回答by Mauren
You must include iostreamin order to use cerr.
See http://en.cppreference.com/w/cpp/io/basic_ostream.
您必须包含iostream才能使用cerr.
请参阅http://en.cppreference.com/w/cpp/io/basic_ostream。
回答by B?ови?
You need to add this at the top :
您需要在顶部添加：
#include <iostream>
for cerr and endl
对于 cerr 和 endl
回答by jilles de wit
回答by user195257
#include <fstream>
#include <iostream>
#include "basic.h"
std::ostream& operator<<(std::ostream &out, Basic const &x) {
// output stuff: out << x.whatever;
return out;
}
int main() {
using namespace std;
ofstream output ("output.txt", ios::out);
if (!output) { // NOT comparing against NULL
cerr << "File cannot be opened.\n";
return 1;
}
output << "Opening of basic account with a 100 Pound deposit:\n";
Basic myBasic (100);
output << myBasic << endl;
return 0;
}
