Edit txt file to correct object detection results

[danaitri]

Hello all,

I have evaluated an object detection method and I wrote my detection results to a txt file.
The txt file is written in the following format:

0001.jpg
8
716 265 87 87
587 298 95 95
443 320 94 94
327 358 86 85
214 368 100 99
443 324 91 91
590 305 91 91
324 359 92 93
721 260 91 91
207 372 107 106
0002.jpg
8
589 302 89 88
715 266 85 85
0003.jpg
8
588 303 89 89
446 325 87 87
327 360 88 89


which means that in picture 0001.jpg, I have 8 detection bounding boxes and below are their coordinates.
The problem is I made a mistake and instead of writing the correct number of bounding boxes I wrote 8 under every image name. How can I correct my txt file and write the proper
number of bounding boxes by counting the number of boxes under each image name?

For example I want to produce a new txt that will be in the following format:

0001.jpg
10
716 265 87 87
587 298 95 95
443 320 94 94
327 358 86 85
214 368 100 99
443 324 91 91
590 305 91 91
324 359 92 93
721 260 91 91
207 372 107 106
0002.jpg
2
589 302 89 88
715 266 85 85
0003.jpg
3
588 303 89 89
446 325 87 87
327 360 88 89

This is a beginners question but I am having real trouble fixing this and I cant afford to correct the original bug and run the detection experiment again. Thank you in advance any help will be highly appreciated.

[2kaud]

Assuming that these files are indeed text files with each line terminated with a \n and that the first line is the number of remaining lines in the file, then to alter this number the file will have to be read, the new number calculated and then the file re-written with the correct number. As the new number may not have the same number of digits as the existing, it simply can't be overwritten. So consider

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
using namespace std;

int main(int argc, char* argv[])
{
	if (argc != 2) {
		cout << "usage: " << argv[0] << " <filename>" << endl;
		return 1;
	}

	ifstream ifs(argv[1]);

	if (!ifs.is_open()) {
		cout << "Cannot open file " << argv[1] << endl;
		return 2;
	}

	string line;
	vector<string> vs;

	while (getline(ifs, line))
		vs.push_back(line);

	ifs.close();
	vs.erase(vs.begin());

	ofstream ofs(argv[1]);

	if (!ofs.is_open()) {
		cout << "Cannot open file " << argv[1] << endl;
		return 2;
	}

	ofs << vs.size() << endl;

	for (const auto& v : vs)
		ofs << v << endl;

	ofs.close();
}