[英]Problems with dynamic memory allocation for structs in C
我得到了数量未知的“宽符号”。 文本的格式设置为句子,我必须将其添加到结构“文本”中。
这些是我的结构:
struct Sentence {
wchar_t *sentence;
int amount_of_symbols;
};
struct Text {
struct Sentence *sentences;
int amount_of_sentences;
};
我为“句子”结构数组动态分配内存并添加它们。 这是我的输入代码:
int amount_of_sentences = 0;
struct Sentence *sentences = (struct Sentence *) malloc(amount_of_sentences * sizeof(struct Sentence));
struct Text text = {sentences, amount_of_sentences};
wchar_t symbol;
int buffer_size = 0;
wchar_t *buffer = (wchar_t *) malloc(buffer_size * sizeof(wchar_t));
bool sentence_begun = true;
while (true) {
symbol = getwchar();
if (symbol == '\n')
break;
if (sentence_begun && symbol == ' ') {
sentence_begun = false;
continue;
}
buffer = (wchar_t *) realloc(buffer, (++buffer_size) * sizeof(wchar_t));
buffer[buffer_size - 1] = symbol;
if (symbol == '.') {
buffer[buffer_size] = '\0';
text.amount_of_sentences++;
text.sentences = (struct Sentence *) realloc(text.sentences, text.amount_of_sentences * sizeof(struct Sentence));
text.sentences[text.amount_of_sentences - 1].amount_of_symbols = buffer_size;
text.sentences[text.amount_of_sentences - 1].sentence = (wchar_t *) malloc(buffer_size * sizeof(wchar_t));
text.sentences[text.amount_of_sentences - 1].sentence = buffer;
buffer_size = 0;
buffer = (wchar_t *) realloc(buffer, buffer_size * sizeof(wchar_t));
sentence_begun = true;
}
}
一切似乎都很好,但是当我尝试输出所有句子时,并没有全部显示出来,有些重复了。
这是我的输出代码:
for (int i = 0; i < text.amount_of_sentences; i++) {
wprintf(L"%ls\n", text.sentences[i].sentence);
}
输入输出示例:
adjsand. asdad.a.a. aaaa. adsa.
a.
adsa.
adsa.
此代码可能有什么问题,我应该更改什么?
首先,您的缓冲区太小1,并且不考虑终止符'\\0'
。 在程序的顶部,执行以下操作:
int buffer_size = 1;
wchar_t *buffer = (wchar_t *) malloc(buffer_size * sizeof(wchar_t));
*buffer= '\0';
但是真正的问题在于:
text.sentences[text.amount_of_sentences - 1].sentence =
(wchar_t *) malloc(buffer_size * sizeof(wchar_t));
text.sentences[text.amount_of_sentences - 1].sentence = buffer;
buffer_size = 0;
buffer = (wchar_t *) realloc(buffer, buffer_size * sizeof(wchar_t));
您为句子分配内存,但是随后用buffer
指针覆盖了该指针。 接下来,您重置缓冲区大小并重新分配缓冲区。
分配不复制缓冲区中的数据。 为此,请执行以下操作:
strcpy(text.sentences[text.amount_of_sentences - 1].sentence, buffer);
在这里,也要做:
buffer_size = 1;
buffer = (wchar_t *) realloc(buffer, buffer_size * sizeof(wchar_t));
*buffer= '\0';
问题在这里。
text.sentences[text.amount_of_sentences - 1].sentence = (wchar_t *) malloc(buffer_size * sizeof(wchar_t));
text.sentences[text.amount_of_sentences - 1].sentence = buffer;
buffer_size = 0;
buffer = (wchar_t *) realloc(buffer, buffer_size * sizeof(wchar_t));
您可以使用malloc
分配一个新语句,然后使用buffer
覆盖它。 这将泄漏内存。
然后,将buffer
分配给text.sentences[text.amount_of_sentences - 1].sentence
,然后通过重新分配buffer
释放该内存。
从C标准...
realloc函数取消分配ptr指向的旧对象,并返回一个指向具有size指定大小的新对象的指针。
text.sentences[text.amount_of_sentences - 1].sentence
指向已释放的内存。 这将导致不确定的行为。
而是指向buffer
并分配一个新的buffer
。
text.sentences[text.amount_of_sentences - 1].sentence = buffer;
buffer_size = 0;
buffer = malloc(buffer_size * sizeof(wchar_t));
其他注意事项...
如Paul所述 ,您需要为空字节分配一个额外的字节。
在堆栈上分配一个较大的缓冲区以读取输入(如果需要的话,增加它)是更简单,更快和更不容易出错的错误。 然后将内容复制到适当大小的内存中。
我继续编写了一个改进的版本进行说明。 如果这是家庭作业,请不要上交。
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