我有两个这样的文本文件：11.txt：
1 5.66
2 4.95
3 2.55
4 0.99
5 2.87
NB.txt：
1 2 3 4 5
4 5 3 2 1
3 4 5 1 2
我已经编写了下面的代码，例如，从文件1中选择“ 1”，然后在文件2中进行搜索，然后将“ 1”替换为“ 5.66”。并重复其他数字，即2,3,4,5。但我不知道为什么它不起作用。此外，它不会读取11.txt的第一行。
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main ()
{
string line;
double AtomId, Atom_radius,search ;
ifstream AtomId_file ("11.txt");
string namefile;
if (AtomId_file.is_open()){
for (int linenox = 0; getline (AtomId_file,line) && linenox < 6; linenox++){
if (linenox == 0) AtomId_file>>AtomId>>Atom_radius;
}
cout<<"AtomId: "<<AtomId<<" Atom_radius: "<<Atom_radius<<endl;
cout<<namefile<<"\n";
}
ifstream NB("NB.txt");
size_t pos;
if (NB.is_open())
{
search = AtomId;
getline(NB,line);
pos=line.find(search);
if(pos!=string::npos)
{
search = Atom_radius;
cout <<"Found!";
}
}
ofstream myfile;
myfile.open ("12.txt");
myfile << search << "\n";
}
12.txt中的输出是：
2
而不是：
5.66 4.95 2.55 0.99 2.87
0.99 2.87 2.55 4.95 5.66
2.55 0.99 2.87 5.66 4.95
我了解您是C ++的新手。
我分析了您的代码，并在错误所在的地方添加了大量注释。您需要更改设计。在开始键入代码之前，您必须先写下，what应该完成。然后，这是最重要的，您认为（不考虑任何语言）如何就可以解决问题。这是最重要的。也适合您以后的编程生涯。 design最重要。因此，请考虑3个小时，该怎么做。在互联网上搜索可能的设计解决方案。将其写在纸上或其他地方。
然后，经过数小时的思考，选择一种合适的语言并检查其实施方式。
我在下面显示了标准的C ++解决方案。您不会立即了解它。因此，请首先尝试理解design。然后在互联网上查找所有使用过的C ++语句并尝试理解。
在开始编写代码之前，请阅读一些不错的C ++书籍。
请先查看您的注释代码：
#include <iostream>
#include <fstream>
#include <string>
using namespace std; // You should not use this line at all. Use qualified names.
int main()
{
string line;
double AtomId, Atom_radius, search; // These variables are not initalized
ifstream AtomId_file("r:\\11.txt");
string namefile;
if (AtomId_file.is_open()) { // You should not use is_open but simply if (AtomId_file)
// Here you have a loop running from 0,1,2,3,4,5. That are 6 loops. But you have only 5 lines in your sourcefile
// The you read one line, each time the loops runs. So in the beginning, this will read the first line
for (int linenox = 0; getline(AtomId_file, line) && linenox < 6; linenox++) {
// And only for the first loop event, when linenox==0, you read then next line "2 4.95"
// So you read already lines. But not more.
// ypu need to read line by line (only one per loop) and then store the result in an appropriate STL Container
if (linenox == 0) AtomId_file >> AtomId >> Atom_radius;
}
// Since you assigned the data only once, the values will be 2, 4.95
// They will never change
cout << "AtomId: " << AtomId << " Atom_radius: " << Atom_radius << endl;
// The variable namefile has never been initailized and is always emtpy, So ""
cout << namefile << "\n";
}
ifstream NB("r:\\NB.txt");
size_t pos; // Not initialized
if (NB.is_open()) // Not recommended. Use "if (NB) instead". In general, use more meaningful variable names
{
search = AtomId; // search is now 2 and never somthing else
getline(NB, line); // Read exactly one (and only this one time) a line containing 1, 5.66
pos = line.find(search); // So, 2 will never be found
if (pos != string::npos) // Always false, can never be true
{
search = Atom_radius; // Will never be executed
cout << "Found!"; // Will never be executed
}
}
ofstream myfile; // You can write directly ofstream myfile("12.txt");
myfile.open("12.txt");
myfile << search << "\n"; // And the output will always be 2.
}
这是一个正确且有效的示例：
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <unordered_map>
#include <vector>
#include <iterator>
int main() {
// Open the file 11.txt and check, if it could be opened
if (std::ifstream file11("11.txt"); file11) {
// Define variable id and attribute and initialize them to theire default values.
unsigned int id{};
double attribute{};
// Here we will store all values (id, attribute) of all lines that we read in the follwing loop
std::unordered_map<unsigned, double> replacement{};
// Read in a llop ALL lines and extract id and attribute, and, check if this worked
while (file11 >> id >> attribute) {
// Create a new replacement value for id
replacement[id] = attribute;
}
// So, now, all data from file 11.txt is read and stored.
// We will now read the next file and store the data
// Open next input file NB.txt and check, if that worked
if (std::ifstream fileNB("NB.txt"); fileNB) {
// And already now, open output file 12.txt and check, if open worked
if (std::ofstream myfile("12.txt"); myfile) {
// Read a complete line and check, if that worked. Read all lines in a loop
for (std::string line; std::getline(fileNB, line); ) {
// Put the line in a std::istringstream, so that we can extract each single value
std::istringstream iss(line);
// We will store the single values of the just read line into a vector
// This we do, because we do not know, how many values will be in that line
// We use a so called iterator, to iterate over all elements in the just read line
// The result will be stored in a vector
// The istream_iterator will call the ">>"-operator, until the line is empty
// For the vector, we use its range constructor
std::vector values(std::istream_iterator<unsigned>(iss), {});
// Now go through all values, replace them and out the result into the output file
for (const unsigned& u : values) myfile << replacement[u] << " ";
myfile << "\n";
}
}
}
}
return 0;
}
当然还有许多其他可能的解决方案
[打开文件时，请指定文件的完整路径，并始终检查文件是否<：
ifstream is11{ "c:/temp/11.txt" };
if (!is11)
return cout << "could not open input", -1;
索引和值组成。这应该使您认为“向量/数组”。读取索引和值，然后将值存储在std::vector中。如果您不知道如何使用它，只要输入文件中的索引在限制范围之内，plain array就足够了–如果文件中的最大索引为10，则为数组大小必须至少为11。
double input[1024];
int idx;
double value;
while (is11 >> idx >> value) // while we can read
input[idx] = value;
寻找值并将其写入。
while (isnb >> idx)
os12 << input[idx] << ' ';