将 output 从 function 重定向到 C 中的文件

Question

I want to redirect some printf() from a function to a file.

I dont want to change the whole function. Instead I want something like this:

 void write_to_temp_File(struct s_28b_meta, struct s_db_entry);

file_name = "temp.txt";
handle_file = CreateFile(file_name, GENERIC_WRITE, 0,NULL, CREATE_ALWAYS, NULL);

//sanity check
if(handle_file == INVALID_HANDLE_VALUE)
printf("Could not open %s file, error %d\n", file_name, GetLastError());

//test check
test = GetHandleInformation(handle_file, lpdwFlags);
printf("The return value is %d, error %d\n", test, GetLastError());

//actually print into file
fprintf(handle_file, reader_print_db(byte **ptr_to_s_20b_parse_entries, 1024));

//clean close and exit
CloseHandle(handle_file);
return 0;

So in fact, I want to open a file and redirect the output of all prints inside the function to the new created file.

In sysCall it would be something like:

text.exe > temp.txt

Is there a good way to do it and how can I get the length of the output of the function, instead of a static value like I have?

Thank you already

Answer 1

using freopen should help you.

freopen("temp.txt", "a+", stdout);

After reopening the stdout with freopen() all output statement printf, putchar are redirected to file temp.txt . So after that any printf() statement will redirect it's output to the temp.txt file.

reference: https://linux.die.net/man/3/freopen