我有2个文本文件，output文本文件和输入文本文件，我怎么append输入文本文件在output文本文件开头的行（c++）？

Question

file.open(input_file);
char z;
while(file.get(z))
{
    str1 = str1 + z;
    pos1++;
} 
file.close();
fout.open(output_file , ios :: app);
file.seekg(0,ios::beg) ;
fout<<endl;
fout<<str1;
fout.close();

file.open(output_file);
file.seekg(0,ios::beg);

char y;
while(file.get(y))
{
    cout<<y;
}
file.close();
cout<<endl;

In the above code, I have used seekg and std::ios::app function but it adds the input text file at the end of output text file. How do I add it at the beginning?

Answer 1

Not tested, but I get:

file.open(input_file);
char z;
while(file.get(z))
{
    str1 = str1 + z;
    pos1++;
} 
file.close();
fout.open(output_file , ios :: app);
char y;
while(file.get(y))
{
    fout<<y;
}
fout<<endl;
fout<<str1;
fout<<endl;
file.close();

For some dumb reason, OS's almost never provide means to prepend a file, I suppose thinking to prevent half-empty sectors; so you must re-write it all. Also, you might want to limit the amount of input, so as to not cause a buffer overflow security risk or memory access crash. Also, block I/O is much faster.