c++ vector bad access | 易学教程

问题

Hi I have the following c++ program:

#include <iostream>
#include <fstream>
#include <vector>
#include <sstream>
#include <boost/foreach.hpp>
#include <stdexcept>
#include <boost/flyweight.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/filesystem.hpp>

namespace fs = boost::filesystem;

struct entry
{
int file;
std::vector<double> a;
};


void my_file(const std::string&file, std::vector<entry> &data, int i){
try{
    std::ifstream in(file.c_str());
    entry e;
    std::string line;
    e.file = i;
    while(getline(in,line)){
        try{
            data[i].a.push_back( boost::lexical_cast<double> (line));
        }catch(boost::bad_lexical_cast bad){
            //std::cerr << bad.what() << std::endl;
        }
    }
}catch(std::runtime_error err){
    std::cerr << err.what() << std::endl;
}

}

void write_file(const std::string &file,std::vector<entry> data,const char* t_path){
try{
    std::string new_file = t_path ;
    new_file = new_file + "/" + file;
    std::ofstream f(new_file.c_str());

    for(size_t i = 0 ;i < data[1].a.size();i++){
        std::cout << "i: " << i;
        for(size_t j = 1; j < data.size();j++){
            std::cout << "j: " << j << std::endl;
            f << data[j].a[i]<< "\t";
        }
        f << "\n";
    }

}catch(std::runtime_error err){
    std::cerr << err.what()<< std::endl;
}
}


int collect_peak(const char*argv,const char*out){
std::cout << "collecting peaks\n";
std::stringstream sstr(argv);
std::string _line;
int c = 0;
std::vector<std::string> files;

while (getline(sstr,_line)){
    std::cout << _line << std::endl;
    fs::path p(_line);
    std::string tmp = p.parent_path().string() +"/_peak_" +      p.filename().string();
    files.push_back(tmp);
    c++;
}

std::cout << "c: " << c << std::endl;
std::vector<entry> data;
for (int i=0 ; i < files.size() ;++i){
    std::cout << files[i] <<std::endl;
    my_file(files[i],data,i);
}
write_file("__peak.txt",data,out);
return 0;

}

Somehow it always gives me a bad access in the my_file method. The program should actually to the following:

read multiple files that contain a caption and ten doubles seperated by a newline
output everything into one file so it looks like this:
1. file \t 2. file \t 3. file \t ...
2. file \t 2. file \t 3. file \t ...
3. file \t 2. file \t 3. file \t ...
4. file \t 2. file \t 3. file \t ...
5. file \t 2. file \t 3. file \t ...

This actually worked already, but i reused it now in a different program. Any ideas?

Thank you

回答1:

This line:

std::vector<entry> data;

creates an empty vector, which you are passing to my_file and accessing data[i] within. You need to reserve space for the elements before you can access arbitrary indices in the vector. For example:

std::vector<entry> data(maxItems);

来源：https://stackoverflow.com/questions/5342596/c-vector-bad-access

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