Related array(s)
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From: Piranha on 28 Dec 2007 10:49 Hello NG, I have some sets of data in a file, containing an int and a string per line. Obviously its a file, so on start all string(s), but I have to convert the first entry to int, because I need some mathematical operations with it. The amount of lines is variable same as the length of the string(s). Example: 123 some text 345 some other text I would like to create an array out of it that allows me to: - search a specific int and output the related string - skip a specific int and output the remaining strings - search a specific text and output the related int Furthermore I need this array so often throughout my script that I would rather create a global array than re-read the file all the time My problems are: - How do I define the array without to know its length? - How do I define the strings within the array without to know their length? - How do I add/delete/modify an entry in the array later on, without to leave blank entries? Usually there will be only 4 or 5 entries, but the max is over 1000, usually a string won´t have more than 15 characters, but the max is much longer, so I think the usual char[max length + 1] would be an awful waste of space 99% of times, also I mostly need a string as std::string, so I might do better with std::string upon reading already, but how to create an array of std::string´s? I´m kinda free on the data format within the file, so if it was easier to separate int and string in the file by some character other than a space, that would be possible
From: Ulrich Eckhardt on 28 Dec 2007 11:39 Piranha wrote: > I have some sets of data in a file, containing an int and a string per > line. > Obviously its a file, so on start all string(s), but I have to convert > the first entry to int, because I need some mathematical operations > with it. > The amount of lines is variable same as the length of the string(s). > > Example: > > 123 some text > 345 some other text > > I would like to create an array out of it Okay, the first question to answer is what language you are writing, because the solutions depend on that. Anyway, the general approach would be to read line by line, convert them into the integer and string they consist of and add them to a container. Note that your approach to use an array already unnecessarily limits your possibilities, maybe a linked list would be the better approach. > that allows me to: > - search a specific int and output the related string > - skip a specific int and output the remaining strings > - search a specific text and output the related int No problem for any kind of container, they only differ in how fast or complicated they are. > My problems are: > - How do I define the array without to know its length? For C++, take a look at e.g. std::vector<>, for C take a look at malloc()/realloc()/free(). > - How do I define the strings within the array without to know their > length? Strings are only variable-length containers for chars. In C, you would use the same functions as above, in C++ you would use std::string though. > - How do I add/delete/modify an entry in the array later on, without > to leave blank entries? In an array, you can't easily do that. What you can do is swap the element to delete with the last one, so you only have blanks at the end. Otherwise, it means copying each element to the one before in order to fill the gap. This is much easier with a linked list. > Usually there will be only 4 or 5 entries, but the max is over 1000, > usually a string won�t have more than 15 characters, but the max is > much longer, > so I think the usual > char[max length + 1] > would be an awful waste of space 99% of times, > also I mostly need a string as std::string, so I might do better with > std::string upon reading already, but how to create an array of > std::string�s? Ah, so you are using C++. Well, I think you don't want an array of strings but rather an array of a string and an integer each, for which you use a struct. Now, if you know how to create an array of ints, you simply replace 'int' with some other type to get an array of a different type. Note that there are several different things here that you should tackle separately, e.g. using structures, using container template classes, using the std::string class, reading files line by line and parsing each line. Uli
From: Ivan Novick on 28 Dec 2007 11:39 On Dec 28, 7:49 am, Piranha <eu_pira...(a)gmx.net> wrote: > 123 some text > 345 some other text > > I would like to create an array out of it that allows me to: > - search a specific int and output the related string > - skip a specific int and output the remaining strings > - search a specific text and output the related int Read in each line of text into a std::string using std::getline. For each line split the line into an int and a string using std::istringstream. Than for each line put the data into 2 std::map's. one where the key is a string and the other where the key is the int. Than do whatever you want to with the data. As a side note writing "scripts" like this in perl is trivial... its basically the exact problem perl is designed for. Regards, Ivan Novick http://www.0x4849.net
From: Piranha on 28 Dec 2007 12:44 On 28 Dez., 17:39, Ulrich Eckhardt <dooms...(a)knuut.de> wrote: > Now, if you know how to create an array of ints, you simply > replace 'int' with some other type to get an array of a different type. > There I got my problem with the size of the array, the only way I know of, how to create an array of std::string´s is std::string mystringarray[] = { std::string(""), std::string(""), std::string("") } Thats easy to handle, but obviously requires to know in advance, how many entries the array has, it allows deleting, modifying or loop through the entries, but no add and for an array of over 1000 entries, this way of declaration is not really practical anymore
From: Piranha on 28 Dec 2007 13:05
On 28 Dez., 17:39, Ivan Novick <i...(a)0x4849.net> wrote: > > Read in each line of text into a std::string using std::getline. > > For each line split the line into an int and a string using > std::istringstream. > > Than for each line put the data into 2 std::map's. one where the key > is a string and the other where the key is the int. > > Than do whatever you want to with the data. > > As a side note writing "scripts" like this in perl is trivial... its > basically the exact problem perl is designed for. > Thanks for the answer, and nice guess :) I´m actually trying to convert a php script I´ve written long ago and implement it into a C++ application. In php I´ve written this in a few minutes, no need to declare anything before first use, no need to convert string to int, etc. I can simply create one single array, fill it with all data, and end up with an array where all even entries are my int´s and entry + 1 is the related string I can add an entry as aray[count(array)] = newEntry and so on But in C/C++ I´m a beginner and I´m trying to figure out what all I need to declare everything before first use, convert everything to the required type and (biggest problem) if I need 2 separate arrays for int and string, then how do I make sure I don´t lose the relations? |