C++ 读取行和写入文件(行卫生)

Question

我的部分代码似乎遇到了一些奇怪的问题，这些问题涉及从现有文件读取一行并将一部分写入另一个文件:

这是我所看到的示例(我只想要元音)。

这是我的三个函数。在尝试找出原因时，我有点 .c_str() 高兴:

void do_file_magic(string file){
    fstream source;
    string outfile,
               line,
               vowels,
               temp;

    // Name the outfile
    outfile = "vowels_" + file;

    source.open(file);
    if (!source.is_open()) {
        die_a_clean_death("Unable to open source file:", file);
    };

    ofstream destination(outfile);
    if (!destination.is_open()) {
        source.close();
        die_a_clean_death("Unable to open destination file:", file);
    };

    // read source file and output vowels to destination file.
    do {
        for (int i = 1; !source.eof(); i++ ){
            getline(source, line);
            temp = vowels_on_a_line(line) + "\n";
            destination << temp.c_str();
        };
    } while (!source.eof());

    // Close the files
    source.close();
    destination.close();
};

string vowels_on_a_line(string input){
    int input_size = input.size(),
    vowel_counter = 0;

    // this will not be larger than input_size
    char vowelarray[input_size];

    // find the vowels with the vowel test
    for (int i = 0; i < input_size; i++){
        if (vowel_test(input[i])){
            vowelarray[vowel_counter] = input[i];
            vowel_counter++;
        };
    };

    // convert array to string
    string vowels(vowelarray);

    // return the 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;
    };
};

有没有人看到我在这里做错了什么？

这是运行时的终端输出。我注意到有 ?U? 代替文本编辑器输出:

Mac Shell: Homework2/>$ ./Homework2 

Enter a 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/>$

Answer 1

显示的代码中存在多个错误。

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

在循环条件中检查 eof() is always a bug.

 char vowelarray[input_size];

 // You put something into vowelarray.

 string vowels(vowelarray);

显示的代码实例化了 vowelarray。 vowelarray 未初始化。随后的代码继续填充 vowealarray 的初始内容。

将 vowelarray 传递给 std::string 的构造函数会将 char 数组衰减为 const char * .

std::string 构造函数的 const char * 参数必须是一个以“\0”结尾的字符串。

显示的代码无法以 \0 字节终止字符串。因此，生成的字符串通常会包含随机垃圾，这就是您所看到的。

您需要将数组的最大大小增加 1，以考虑额外的 '\0' 字符:

char vowelarray[input_size+1];

然后在从中构造 std::string 之前，将终止符 '\0' 正确添加到 char 数组。