c - 使用 malloc() 和 free() 的程序崩溃

Question

在尝试释放内存部分时，我的程序似乎崩溃了。以下是我的链表的整体结构:

typedef struct {
    char                            *dataitem;
    struct listelement              *link;
    int16_t                         wordSize;
    int16_t                         (*libWord)[Q];
    char                            gpioValue;
    struct listelement              *syllables;
}listelement;

调用此函数时程序崩溃:

recordedWordsPointer = RemoveItem(recordedWordsPointer);                            // get rid of any junk stored in the recorded buffer

地点:

volatile listelement *recordedWordsPointer;

在 libWord 中存储了值，如果有另一个链接则指向下一个链接，否则为 NULL。下面显示了进入该函数时发生的情况:

listelement * RemoveItem (listelement * listpointer) {
    cpu_irq_disable();
    listelement * tempp = listpointer;

    while( listpointer->syllables != NULL ){
        RemoveSyllable(listpointer->syllables);
    }
    if( listpointer != NULL ){
        tempp = listpointer -> link;
        free (listpointer->dataitem);
        free (listpointer->libWord);
        free (listpointer);
    }
    cpu_irq_enable();   
    return tempp;
}

void RemoveSyllable (listelement * listpointer) {

    while( listpointer->syllables != NULL ){
        RemoveSyllable(listpointer->syllables);
    }
    free (listpointer->dataitem);
    free (listpointer->libWord);
    free (listpointer);
    listpointer = NULL;
    return;
}

我想知道我是否做错了什么导致内存崩溃？

谢谢!

编辑:

我被要求展示我如何构造内存位置来提供帮助。我使用以下两个函数:

listelement * AddItem (listelement * listpointer, char* name, int16_t size, int16_t wordLength, int16_t (*words)[Q]) {
    // returns listPointer at the beginning of list
    listelement * lp = listpointer;
    listelement * listPointerTemp;
    char ErrorHandler = NULL;
    // are we at the end of the list?
    if (listpointer != NULL) {
        // move down to the end of the list
        while (listpointer -> link != NULL)
        listpointer = listpointer -> link;
        listPointerTemp = listpointer;
        listpointer -> link = (struct listelement  *) malloc (sizeof (listelement));
        // on fail end links becomes NULL already above
        if(listpointer -> link != NULL){
            listpointer = listpointer -> link;
            listpointer -> link = NULL;
            listpointer -> wordSize = wordLength;
            listpointer -> syllables = NULL;

            listpointer -> dataitem = (char*) malloc ((size + 1)*sizeof(char));
            if(listpointer -> dataitem != NULL){
                for(int i=0; i<size ; i++){
                    listpointer -> dataitem[i] = name[i];
                }
                listpointer -> dataitem[size] = NULL;

                listpointer -> libWord =  (int16_t(*)[Q])malloc(wordLength*Q*sizeof(int16_t));
                if(listpointer -> libWord != NULL){
                    for (int16_t row=0 ; row < wordLength ; row++){
                        for (int col=0 ; col < Q ; col++){
                            listpointer -> libWord[row][col]  = words[row][col];
                        }
                    }
                    ErrorHandler = 1;
                }else{
                    free(listpointer->dataitem);
                    free(listpointer);
                    listPointerTemp -> link = NULL;
                }
            }else{
                free(listpointer);
                listPointerTemp -> link = NULL;
            }
        }
        if(ErrorHandler == NULL){
            //failure
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
            usart_write_line(&AVR32_USART0,"Ran out of Memory!  Word not created.\r\n");
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
        }
        return lp;
    } else {
        listpointer = (struct listelement  *) malloc (sizeof (listelement));

        if(listpointer != NULL){
            listpointer -> link = NULL;
            listpointer -> wordSize = wordLength;
            listpointer -> syllables = NULL;

            listpointer -> dataitem = (char*) malloc ((size + 1)*sizeof(char));
            if(listpointer -> dataitem != NULL){
                for(int16_t i=0; i<size ; i++){
                    listpointer -> dataitem[i] = name[i];
                }
                listpointer -> dataitem[size] = NULL;

                listpointer -> libWord =  (int16_t(*)[Q])malloc(wordLength*Q*sizeof(int16_t));
                if(listpointer -> libWord != NULL){
                    for (int16_t row=0 ; row < wordLength ; row++){
                        for (int col=0 ; col < Q ; col++){
                            listpointer -> libWord[row][col]  = words[row][col];
                        }
                    }
                    ErrorHandler = 1;
                }else{
                    free(listpointer->dataitem);
                    free(listpointer);
                    listPointerTemp -> link = NULL;
                }
            }else{
                free(listpointer);
                listPointerTemp -> link = NULL;
            }
        }
        if(ErrorHandler == NULL){
            //failure
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
            usart_write_line(&AVR32_USART0,"Ran out of Memory!  Word not created.\r\n");
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
        }
        return listpointer;
    }
}

listelement* AddSyllable (listelement * listpointer, char* name, int16_t size, int16_t wordLength, int16_t (*words)[Q]) {
    // returns listPointer at the beginning of list
    listelement * lp = listpointer;
    listelement * listPointerTemp;
    char ErrorHandler = NULL;
    // are we at the end of the list?
    if (listpointer != NULL) {
        // move down to the end of the list
        while (listpointer -> syllables != NULL)
        listpointer = listpointer -> syllables;
        listPointerTemp = listpointer;
        listpointer -> syllables = (struct listelement  *) malloc (sizeof (listelement));
        // on fail end links becomes NULL already above
        if(listpointer -> syllables != NULL){
            listpointer = listpointer -> syllables;
            listpointer -> link = NULL;
            listpointer -> wordSize = wordLength;

            listpointer -> dataitem = (char*) malloc ((size + 1)*sizeof(char));
            if(listpointer -> dataitem != NULL){
                for(int i=0; i<size ; i++){
                    listpointer -> dataitem[i] = name[i];
                }
                listpointer -> dataitem[size] = NULL;

                listpointer -> libWord =  (int16_t(*)[Q])malloc(wordLength*Q*sizeof(int16_t));
                if(listpointer -> libWord != NULL){
                    for (int16_t row=0 ; row < wordLength ; row++){
                        for (int col=0 ; col < Q ; col++){
                            listpointer -> libWord[row][col]  = words[row][col];
                        }
                    }
                    ErrorHandler = 1;
                }else{
                    free(listpointer->dataitem);
                    free(listpointer);
                    listPointerTemp -> syllables = NULL;
                }
            }else{
                free(listpointer);
                listPointerTemp -> syllables = NULL;
            }
        }
        if(ErrorHandler == NULL){
            //failure
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
            usart_write_line(&AVR32_USART0,"Ran out of Memory!  Word not created.\r\n");
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
        }
        return lp;
    } else {
        listpointer = (struct listelement  *) malloc (sizeof (listelement));

        if(listpointer != NULL){
            listpointer -> link = NULL;
            listpointer -> wordSize = wordLength;

            listpointer -> dataitem = (char*) malloc ((size + 1)*sizeof(char));
            if(listpointer -> dataitem != NULL){
                for(int16_t i=0; i<size ; i++){
                    listpointer -> dataitem[i] = name[i];
                }
                listpointer -> dataitem[size] = NULL;

                listpointer -> libWord =  (int16_t(*)[Q])malloc(wordLength*Q*sizeof(int16_t));
                if(listpointer -> libWord != NULL){
                    for (int16_t row=0 ; row < wordLength ; row++){
                        for (int col=0 ; col < Q ; col++){
                            listpointer -> libWord[row][col]  = words[row][col];
                        }
                    }
                    ErrorHandler = 1;
                }else{
                    free(listpointer->dataitem);
                    free(listpointer);
                    listPointerTemp -> syllables = NULL;
                }
            }else{
                free(listpointer);
                listPointerTemp -> syllables = NULL;
            }
        }
        if(ErrorHandler == NULL){
            //failure
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
            usart_write_line(&AVR32_USART0,"Ran out of Memory!  Word not created.\r\n");
            usart_write_line(&AVR32_USART0,"\r\n--------------------------------------------\r\n");
        }
        return listpointer;
    }
}

Answer 1

您的 RemoveSyllable 函数实际上并未将 syllables 成员设置为 NULL。您认为它在例程内部确实如此，但实际上您只是在局部变量内部更改它的值。