C++ readline and write to file (line sanitation) -

i seem running odd issues portion of code involves reading line existing file , writing portion file:

here example of seeing (i want vowels).

here 3 functions involved this. got little .c_str() happy while trying figure out cause:

void do_file_magic(string file){     fstream source;     string outfile,                line,                vowels,                temp;      // name outfile     outfile = "vowels_" + file;      source.open(file);     if (!source.is_open()) {         die_a_clean_death("unable open source file:", file);     };      ofstream destination(outfile);     if (!destination.is_open()) {         source.close();         die_a_clean_death("unable open destination file:", file);     };      // read source file , output vowels destination file.     {         (int = 1; !source.eof(); i++ ){             getline(source, line);             temp = vowels_on_a_line(line) + "\n";             destination << temp.c_str();         };     } while (!source.eof());      // close files     source.close();     destination.close(); };  string vowels_on_a_line(string input){     int input_size = input.size(),     vowel_counter = 0;      // not larger input_size     char vowelarray[input_size];      // find vowels vowel test     (int = 0; < input_size; i++){         if (vowel_test(input[i])){             vowelarray[vowel_counter] = input[i];             vowel_counter++;         };     };      // convert array string     string vowels(vowelarray);      // return stringi     printf("%s\n", vowels.c_str());     return vowels; };  bool vowel_test(char c){     if(         c=='a'||c=='a'||         c=='e'||c=='e'||         c=='i'||c=='i'||         c=='o'||c=='o'||         c=='u'||c=='u'     ) {         return true;     } else {         return false;     }; }; 

does see doing wrong here?

here terminal output while running this. note there ?u? in lieu of text editor output:

mac shell: homework2/>$ ./homework2   enter filename: ----------------- test.txt oeiuooiaeoeeuaiiieiaeeaiiaoeiea uueeaoaeaoiouaiueeiiuaeeeueiiueia?u? uuoeuaeoeiiuoeeauueuiuioiiuieiuuaaoi? aeueeieoioooeauaieoaiuiaeuaoeuaiiu?u? oieuuuiiauoeuoiiaeieieiaeuaaiii ueaooaiuaeuueieieiauiiaieeoioeieiiue? aueuuuuaueieuiaaeuaauaeeeaeeeeuee?u? aauueiuauaiuoeieeoeeooiiuiiaiaueiuuo? aeieeaiaieouo  auiooiiaeauiaeuuuaeeuouuaaauoua eueuoeeuiaeeuuaoiiiuoeieuiuaue iaeeoaoiaieoiauiuauouiaeiaeuuoi eueeeueeeiueeieuioauieeuaeuaa ? iaueeiaeeeueuaoeauueuiauiiauiuieuu?u? eeeueeeoaeuoioiuiauioeieueiua eeeuiiieaeeoiiuioueiaoaiuaaiiai aeaiaeiuauaeeauieoiaeeiiuieeeuui??u? aiuaaaeuaaoooiouiaiaaiueaeuaa ? aeeeueuouauueauaeeuueeoieueioioeua?u? eeaueueiuaaeuuuooeeeiuaeuuiie auiieuioeuaaaaieieeeeuiaiieieeuiee?u? aeaieaeiiaeuaoeauieiuaeueieeeeueua?u? uoueuuuiaai  euaeioaeuieuiaeaiiaiaeoiouaiuaeeeuauue iauoieuauiuaeauaoeaeeaiiauiuueaiueoe? eaiiaeieiuuoueaeeieuuaoeaeeaiuuaea#  iieuoeuaeeaaueiauiieuaoeaiueaaeoi?u? auiaeaeiaeeuiauioeiieiieaaoeeuioeeu  uieueeeueuieoeuauiieauieeiueaiueuiiu? eiuuoiuiieooaaiuiauoaeeiuaiaeuio??u? h?u? mac shell: homework2/>$ 

there multiple bugs in shown code.

   (int = 1; !source.eof(); i++ ){          getline(source, line); 

checking eof() in loop condition is bug.

 char vowelarray[input_size];   // put vowelarray.   string vowels(vowelarray); 

the shown code instantiates vowelarray. vowelarray not initialized. subsequent code proceeds fill initial contents of vowealarray.

passing vowelarray std::string's constructor decays char array const char *.

the const char * parameter std::string constructor must `\0'-terminated string.

the shown code fails terminate string \0 byte. such resulting string typically contain random garbage, you're seeing.

you need increase maximum size of array 1, in order account '\0' character:

char vowelarray[input_size+1]; 

and add terminating '\0' char array, before constructing std::string it.