I have a data_base.txt file with the next structure:
1|client_name|id_client|account_client|balance|status
2|client_name|id_client|account_client|balance|status
Example:
1|John Doe|08913835P|053-323-192|120.00|active
Now I want to have the next four functions working with this file:
This function will add a new client to the .txt file
int newClient(string client_name, string id_client)
{
.....
}
This function will check if a client exists by checking id_client
int checkClient(string id_client)
{
// return true; (if client with that ID exists)
// return false; (if client not exists)
}
This function will get a specific value:
int getData(string field, string id_client)
{
// Example: if string field == 'balance' and id_client == '08913835P' then return '120.00'
// This example is done using above example data structure.
}
This function will modify data
int modifyData(string field, string data)
{
// This should work like the previous function but this function will edit specific values.
}
That's all, I had been Googling for hours and I can't figure out yet how to do this.
This is problematic and horribly inefficient if not done right.
The short answer is that, if the length of each line can change, then you need to completely rewrite the entire file to update the data. This would work, for example, if your program loaded the entire file into memory and then saved it after it was modified.
To update the file on disk, you have to impose some type of rule, such as every line must be the same length. This would mean setting a maximum length for all your fields, and padding those fields with spaces or some other character.
Using the latter technique, it should be possible to construct a new line of data (with padding), know the location of that line in the file (line number - 1 times the length of each line), jump to that location and then write the line.
Getting the data would be simpler but similar. Just determine the offset of the line and read it (you'll know how long the lines is). Strip any padding before presenting to the user.
Modifying a line would be similar to a combination of getting the data and writing the data. You'd just update the data between the two.
Related
So, I have created a program that creates a separate file for every individual student to store his data. I have set a bool variable to restrict accessing data without entring it but it only allows me to get data if I stored it first while I run the program but I restart the program multiple times which means it won't let me get data if I entered it in the previous run as it thinks that I never entered the data. So I want to add a simple (strictly) function/check that checks whether a file was created in the past (in the previous run) or not if yes then it should let me access that data and (if possible) tell me the name of the file so that I can easily access it and if not then it should give me the default error that I coded.
if (first_entry == false)
{
cout << "Enter data first.\n";
system("pause");
goto main;
}
Also, I am using switch statements so in case 1: I ask for data also making >> first_entry = true.
In case 2: I have the check that I have mentioned above if true it displays data from the desired file.
Yes, there is a way to check if file exists. You will have to know it's name first, though. I guess that since you have some files already created, then you have your data stored in some sort of array / other structure and based on that you can guess the name of the file.
Anyways, here's the code:
#include <fstream>
...
fstream file;
file.open("directory/your_file.txt", ios::in); //this is where you
//need to know the filename
if(file.good()) // <-- if file stream returns 'goodbit' iostate
// which means "does this file open and contain some data"
{
/* handle data */
}
You can find more about good() here.
Since you already use system(), you can also echo out content of directory
using basic windows shell commands, but it seems to be a workaround-like bad solution.
I am serializing multiple objects and want to save the given Strings to a file. The structure is the following:
A few string and long attributes, then a variable amount of maps<long, map<string, variant> >. My first idea was creating one valid JSONFile but this is very hard to do (all of the maps are very big and my temporary memory is not big enough). Since I cant serialize everything together I have to do it piece by piece. I am planning on doing that and I then want to save the recieved strings to a file. Here is how it will look like:
{ "Name": "StackOverflow"}
{"map1": //map here}
{"map2": //map here}
As you can see this is not one valid JSON object but 3 valid JSONObjects in one file. Now I want to deserialize and I need to give a valid JSONObject to the deserializer. I already save tellp() everytime when I write a new JSONObject to file, so in this example I would have the following adresses saved: 26, endofmap1, endofmap2.
Here is what I want to do: I want to use these addresses, to extract the strings from the file I wrote to. I need one string which is from 0 to (26-1), one string from 26 to(endofmap1-1) and one string from endofmap1 to (endofmap2-1). Since these strings would be valid JSONObjects i could deserialize them without problem.
How can I do this?
I would create a serialize and deserialize class that you can use as part of a hierarchy.
So for instance, in rough C++ psuedo-code:
class Object : public serialize, deserialize {
public:
int a;
float b;
Compound c;
bool serialize(fstream& fs) {
fs << a;
fs << b;
c->serialize(fs);
fs->flush();
}
// same for deserialize
};
class Compound : serialize, deserialize {
public:
map<> things;
bool serialize(fstream& fs) {
for(thing : things) {
fs << thing;
}
fs->flush();
}
};
With this you can use JSON as the file will be written as your walk the heirarchy.
Update:
To extract a specific string from a file you can use something like this:
// pass in an open stream (streams are good for unit testing!)
std::string extractString(fstream& fs) {
int location = /* the location of the start from file */;
int length = /* length of the string you want to extract */;
std::string str;
str.resize(length);
char* begin = *str.begin();
fs->seekp(location);
fs->read(begin, length);
return str;
}
Based on you saying "my temporary memory is not big enough", I'm going to assume two possibilities (though some kind of code example may help us help you!).
possibility one, the file is too big
The issue you would be facing here isn't a new one - a file too large for memory, assuming your algorithm isn't buffering all the data, and your stack can handle the recursion of course.
On windows you can use the MapViewOfFile function, the MSDN has plenty of detail on that. This function will effectively grab a "view" of a section of a file - allowing you to load enough of the file to modify only what you need, before closing and opening a view at a later offset.
If you are on a different platform, there will be similar functions.
possibility two, you are doing too much at once
The other option is more of a "software engineering" issue. You have so much data then when holding them in your std::maps, you run out of heap-memory.
If this is the case, you are going to need to use some clever thinking - here are some ideas!
Don't load all your data into the maps. wherever the data is coming from, take a CRC, Index, or Filename of the data-source. Store that information in the map, and leave the actual "big strings" on the hard disk. - This way you can load each item of data when you need it.
This works really well for data that needs to be sorted, or correlated.
Process or load your data when you need to write it. If you don't need to sort or correlate the data, why load it into a map beforehand at all? Just load each "big string" of data in sequence, then write them to the file with an ofstream.
I'm making a simple bug tracker and am using a text file as the database. Right now I'm reading in all the information through keys and importing them into specific arrays.
for (int i = 0; i < 5; i++)
{
getline(bugDB, title[i], '#');
getline(bugDB, importance[i], '!');
getline(bugDB, type[i], '$');
getline(bugDB, description[i], '*');
}
Here is what's in my (terribly unreadable) file
Cant jump#Moderate!Bug$Every time I enter the cave of doom, I'm unable
to jump.*Horse too expensive#Moderate!Improvement$The horses cost way
too much gold, please lower the costs.*Crash on startup#Severe!Bug$I'm
crashing on startup on my Win8.1 machine, seems to be a 8.1
bug.*Floating tree at Imperial March#Minimal!Bug$There is a tree
floating about half a foot over the ground near the crafting
area.*Allow us to instance our group#Moderate!Improvement$We would
like a feature that gives us the ability to play with our groups alone
inside dungeons.*
Output:
This works great for me, but I'd like to be able to delete specific bugs. I'd be able to do this by letting the user choose a bug by number, find the corresponding * key, and delete all information until the program reaches the next * key.
I'd appreciate any suggestions, I don't know where to start here.
There is no direct mechanism for deleting some chunk of data from the middle of the file, no delete(file, start, end) function. To perform such a deletion you have to move the data which appears after the region; To delete ten bytes from the middle of a file you'd have to move all of the subsequent bytes back ten, looping over the data, then truncate to make the file ten bytes smaller.
In your case however, you've already written code to parse the file into memory, populating your arrays. Why not just implement a function to write the contents of the arrays back to a file? Truncate the file (open in mode "w" rather than "w+"), loop over the arrays writing their contents back to the file in your preferred format, but skip the entry that you want to delete.
its only possible by manually copying the data from input file to output file and leaving out the entry you want to delete.
but: i strongly encourage the usage of some small database for keeping the informations (look at sqlite)
Also its a bad bugtracker if solving the bug means "delete it from database" (its not even is a tracker). give it a status field (open, refused, duplicate, fixed, working, ...).
Additional remarks:
use one array that keeps some structure with n informations and not n arrays.
please remind that someone may use your delimiter characters in the descriptions (use some uncommon character and replace its usage in saved text)
explanation for 1.:
instead of using
std::vector<std::string> title;
std::vector<int> importance;
std::vector<std::string> description;
define a structure or class and create a vector of this structure.
struct Bug{
std::string title;
int importance; // better define an enum for importance
std::string description;
};
std::vector<Bug> bugs;
This is my first post here, so please bear with me.
I have searched high and low on the internet for an answer, but I've not been able to resolve my issue, so I have decided to write a post here.
I am trying to write(append) to a JSON array on file using C++ and JZON, at intervals of 1 write each second. The JSON file is initially written by a “Prepare” function. Another function is then called each second to a add an array to the JSON file and append an new object to the array every second.
I have tried many things, most of which resulted in all sorts of issues. My latest attempt gave me the best results and this is the code that I have included below. However, the approach I took is very inefficient as I am writing an entire array every second. This is having a massive hit on CPU utilisation as the array grows, but not so much on memory as I had first anticipated.
What I really would like to be able to do is to append to an existing array contained in a JSON file on disk, line by line, rather than having to clear the entire array from the JSON object and rewriting the entire file, each and every second.
I am hoping that some of the geniuses on this website will be able to point me in the right direction.
Thank you very much in advance.
Here is my code:
//Create some object somewhere at the top of the cpp file
Jzon::Object jsonFlight;
Jzon::Array jsonFlightPath;
Jzon::Object jsonCoordinates;
int PrepareFlight(const char* jsonfilename) {
//...SOME PREPARE FUNCTION STUFF GOES HERE...
//Add the Flight Information to the jsonFlight root JSON Object
jsonFlight.Add("Flight Number", flightnum);
jsonFlight.Add("Origin", originicao);
jsonFlight.Add("Destination", desticao);
jsonFlight.Add("Pilot in Command", pic);
//Write the jsonFlight object to a .json file on disk. Filename is passed in as a param of the function.
Jzon::FileWriter::WriteFile(jsonfilename, jsonFlight, Jzon::NoFormat);
return 0;
}
int UpdateJSON_FlightPath(ACFT_PARAM* pS, const char* jsonfilename) {
//Add the current returned coordinates to the jsonCoordinates jzon object
jsonCoordinates.Add("altitude", pS-> altitude);
jsonCoordinates.Add("latitude", pS-> latitude);
jsonCoordinates.Add("longitude", pS-> longitude);
//Add the Coordinates to the FlightPath then clear the coordinates.
jsonFlightPath.Add(jsonCoordinates);
jsonCoordinates.Clear();
//Now add the entire flightpath array to the jsonFlight object.
jsonFlight.Add("Flightpath", jsonFlightPath);
//write the jsonFlight object to a JSON file on disk.
Jzon::FileWriter::WriteFile(jsonfilename, jsonFlight, Jzon::NoFormat);
//Remove the entire jsonFlighPath array from the jsonFlight object to avoid duplicaiton next time the function executes.
jsonFlight.Remove("Flightpath");
return 0;
}
For sure you can do "flat file" storage yourself.. but this is a symptom of needing a database. Something very light like SQLite, or mid-weight & open-source like MySQL, FireBird, or PostgreSQL.
But as to your question:
1) Leave the closing ] bracket off, and just keep the file open & appending -- but if you don't close the file correctly, it will be damaged & need repair to be readable.
2) Your current option -- writing a complete file each time -- isn't safe from data loss either, as the moment you "open to overwrite" you lose all data previously stored in the file. The workaround here, is to rename the old file as a backup before you start writing.
You should also make backup copies of your file, with the first option. (Say at daily intervals). Otherwise data loss is likely to occur eventually -- on Ctrl-C, power loss, program error or system crash.
Of course if you use any of SQLlite, MySQL, Firebird or PostgreSQL all the data-integrity problems will be handled for you.
I'm making simple dll packet sniffer using C++, that will hook to the apps, and write the received packet into INI file. Unfortunately after 20-30 minutes it crashed the main apps.
When the packet is received, receivedPacket() will be called. After 20+ minutes, WriteCount value is around 150,000-200,000.. and starting to get C++ runtime error/crash, GetLastError() code that I get is 0x8, which is ERROR_NOT_ENOUGH_MEMORY, and the WritePrivateProfileStringA() returns 0
void writeToINI(LPCSTR iSec,LPCSTR iKey,int iVal){
sprintf(inival, _T("%d"), iVal);
WritePrivateProfileStringA(iSec,iKey,inival,iniloc);
//sprintf(strc, _T("%d \n"), WriteCount);
//WriteConsole(GetStdHandle(STD_OUTPUT_HANDLE), strc, strlen(strc), 0, 0);
WriteCount++;
}
void receivedPacket(char *packet,WORD size){
switch ( packet[2] )
{
case 0x30:
// Size : 0x5F
ID = *(signed char*)&packet[0x10];
X = *(signed short*)&packet[0x20];
Y = *(signed short*)&packet[0x22];
Z = *(signed short*)&packet[0x24];
sprintf(inisec, _T("PACKET_%d"), (ID+1));
writeToINI(inisec,"id",ID);
writeToINI(inisec,"x",X);
writeToINI(inisec,"y",Y);
writeToINI(inisec,"z",Z);
}
[.....OTHER CASES.....]
}
Thanks :)
WritePrivateProfileString() and GetPrivateProfileString() are very slow (due to parsing INI file each call), instead you can:
use one of existing parsing libraries, but i am not sure about memory efficiency nor supporting sequential write.
write your own sequential INI writter:
read file (or only part, by part, if it is too big)
find section and key (if not found, create new section at end of file, or find insertion position, if you want sorted sections), save file position of key and next key
change value
save (beginning of original file to position of key + actual changed key + position of next key in original file to end of file) (if new section is created at end, you can simply append new section to original file) (if packets rewrite same ID often, you can add padding whitespace after each key, large to hold any value of desired type (example: change X=1---\n to X=100-\n (change - to whitespace), so you have constant size of key, you can update only part of file) )
database, for example MySQL
write binary file (fastest solution) and make program to read values, or to convert to text
Little note: I use GetPrivateProfileString() few years ago to read settings file (about 1KB of size), reading form HDD: 50ms, reading from USB flash disk: 1000ms!, after changing (1. read file to memory 2. run my own parser) it run in 1ms both on HDD and USB.
Thanks for the reply guys, but looks like the problem wasn't come from WritePrivateProfileStringA().
I just need to add extra size in malloc() for the Hook.
:)