添加到文件而不删除里面的内容
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【中文标题】添加到文件而不删除里面的内容【英文标题】:Adding to a file without erasing what is inside 【发布时间】:2019-06-27 04:17:53 【问题描述】:我正在编写一个代码,该代码从用户那里获取一些输入并将其存储在一个文件中。我的代码应该保留旧数据并添加新数据,但是每次我运行代码时,文件中的旧数据都会被新数据替换。
if(input == 1)
outFile.open("personnel2.dat");
int numRecords = 0;
do
cout << "#1 of 7 - Enter Employee Worker ID Code(i.e AF123): ";
cin >> id;
cout << "#2 of 7 - Enter Employee LAST Name: ";
cin >> lastN;
cout << "#3 of 7 - Enter Employee FIRST Name: ";
cin >> firstN;
cout << "#4 of 7 - Enter Employee Work Hours: ";
cin >> workH;
cout << "#5 of 7 - Enter Employee Pay Rate: ";
cin >> payRate;
cout << "#6 of 7 - Enter FEDERAL Tax Rate: ";
cin >> federalTax;
cout << "#7 of 7 - Enter STATE Tax Rate: ";
cin >> stateTax;
outFile << id << " " << lastN << " " << firstN << " " << workH << " " << payRate << " "
<< federalTax << " " << stateTax << "\n";
numRecords++;
cout << "Enter ANOTHER Personnel records? (Y/N): ";
cin >> moreRecords;
while(moreRecords != 'N' && moreRecords != 'n');
outFile.close();
cout << numRecords << " records written to the data file.\n";
【问题讨论】:
C++ fstream overwrite instead of append的可能重复 【参考方案1】:假设 outfile 是 std::ofstream
的实例,其背后的原因是当您在 ofstream
对象上使用 open()
函数时,文件以 ios_base::out 模式打开,该模式强制在插入之前删除以前的内容新的。
为了附加数据,您必须明确指定append
模式。
例子:
#include <fstream> // std::ofstream
int main ()
std::ofstream ofs;
ofs.open ("test.txt", std::ofstream::out | std::ofstream::app);
ofs << " more lorem ipsum";
ofs.close();
return 0;
来源:http://www.cplusplus.com/reference/fstream/ofstream/open/
在你的情况下,你必须以这种方式改变它:
outFile.open("personnel2.dat", std::ofstream::out | std::ofstream::app);
【讨论】:
【参考方案2】:更改outFile.open("personnel2.dat");
到
outFile.open("personnel2.dat", std::fstream::app);
将模式设置为追加,假设您使用的是fstream::open()
。
【讨论】:
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