[英]Problems with dynamic memory allocation for structs in C
我得到了數量未知的“寬符號”。 文本的格式設置為句子,我必須將其添加到結構“文本”中。
這些是我的結構:
struct Sentence {
wchar_t *sentence;
int amount_of_symbols;
};
struct Text {
struct Sentence *sentences;
int amount_of_sentences;
};
我為“句子”結構數組動態分配內存並添加它們。 這是我的輸入代碼:
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,但是當我嘗試輸出所有句子時,並沒有全部顯示出來,有些重復了。
這是我的輸出代碼:
for (int i = 0; i < text.amount_of_sentences; i++) {
wprintf(L"%ls\n", text.sentences[i].sentence);
}
輸入輸出示例:
adjsand. asdad.a.a. aaaa. adsa.
a.
adsa.
adsa.
此代碼可能有什么問題,我應該更改什么?
首先,您的緩沖區太小1,並且不考慮終止符'\\0'
。 在程序的頂部,執行以下操作:
int buffer_size = 1;
wchar_t *buffer = (wchar_t *) malloc(buffer_size * sizeof(wchar_t));
*buffer= '\0';
但是真正的問題在於:
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));
您為句子分配內存,但是隨后用buffer
指針覆蓋了該指針。 接下來,您重置緩沖區大小並重新分配緩沖區。
分配不復制緩沖區中的數據。 為此,請執行以下操作:
strcpy(text.sentences[text.amount_of_sentences - 1].sentence, buffer);
在這里,也要做:
buffer_size = 1;
buffer = (wchar_t *) realloc(buffer, buffer_size * sizeof(wchar_t));
*buffer= '\0';
問題在這里。
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
分配一個新語句,然后使用buffer
覆蓋它。 這將泄漏內存。
然后,將buffer
分配給text.sentences[text.amount_of_sentences - 1].sentence
,然后通過重新分配buffer
釋放該內存。
從C標准...
realloc函數取消分配ptr指向的舊對象,並返回一個指向具有size指定大小的新對象的指針。
text.sentences[text.amount_of_sentences - 1].sentence
指向已釋放的內存。 這將導致不確定的行為。
而是指向buffer
並分配一個新的buffer
。
text.sentences[text.amount_of_sentences - 1].sentence = buffer;
buffer_size = 0;
buffer = malloc(buffer_size * sizeof(wchar_t));
其他注意事項...
如Paul所述 ,您需要為空字節分配一個額外的字節。
在堆棧上分配一個較大的緩沖區以讀取輸入(如果需要的話,增加它)是更簡單,更快和更不容易出錯的錯誤。 然后將內容復制到適當大小的內存中。
我繼續編寫了一個改進的版本進行說明。 如果這是家庭作業,請不要上交。
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