是否可以在 C 中创建动态指针数组？

Question

Basically I need to save a certain number of strings received from stdin in a dynamic list, but the number of strings is different for each node of my list. What I'm trying to do is to have a double pointer to char , so that I can have an array of strings (an array of pointers to char ). But maybe it doesn't work this way.

Simplifying I have:

typedef struct table {
    int rowsNumber;
    char **array;
    struct content * next;
} content;

table* node=NULL;


int main() {
    ...
    nodecreate();
    ..
}

Then I need to create the table, but here is where I'm getting errors.

void nodecreate()
{
    char line[MAXLENGHT];
    scanf("%d", table->rowsNumber);
    for (i=0; i<rowsNumber, i++) {
        fgets(line, MAXLENGHT, stdin);
        node->array[i] = malloc(strlen(line) * sizeof(char));
        strcpy(node->array[i], line);
    }
}

Answer 1

These declarations

typedef struct table {
    int rowsNumber;
    char **array;
    struct content * next;
} content;

table* node=NULL;

are incorrect.

For example in this typedef declaration

typedef struct table {
    int rowsNumber;
    char **array;
    struct content * next;
} content;

there are declared the type struct table its alias content and one more type struct content . The types struct table and struct content are two different types.

For this declaration

table* node=NULL;

the compiler shall issue a message that the name table is not declared.

It seems you mean the following

typedef struct table {
    int rowsNumber;
    char **array;
    struct table *next;
} content;

content *node = NULL;

In this function

void nodecreate()
{
char line[MAXLENGHT];
scanf("%d",table->rowsNumber);
for(i=0;i<rowsNumber,i++){
    fgets(line,MAXLENGHT,stdin);
    node->array[i]=malloc(strlen(line)*sizeof(char));
    strcpy(node->array[i],line);
}

where a closing brace is absent there is used the null pointer node. So the function will at least invoke undefined behavior. The same problem exists with the data member node->array that has an indeterminate value.

To use the function strcpy you need to reserve also a character for the terminating zero character like

    node->array[i]=malloc(strlen(line)*sizeof(char) + 1);

Also pay attention to that after this call of scanf

scanf("%d",table->rowsNumber);

the following first call of fgets will read an empty string (containing only the new line character '\\n' ) because the input buffer will contain the new line character '\\n' . You have to remove it.

In any case the function does not make sense because the function as it is followed from its name nodecreate shall create a new node. So this means as the function does not have parameters that the function shall return a created node that can be added to the list.

Answer 2

malloc the array of pointers first.

//assuming you malloc'd the table somewhere before calling this...
void nodecreate()
{
char line[MAXLENGHT];
scanf("%d",table->rowsNumber);

node->array = malloc(sizeof(char*)*table->rowsNumber);
for(i=0;i<table->rowsNumber,i++){
    fgets(line,MAXLENGHT,stdin);
    node->array[i]=malloc(strlen(line)*sizeof(char));
    strcpy(node->array[i],line);
}

//don't forget to free both every char * and the char ** somewhere...

Answer 3

You cant malloc array[i] if you havent already allocated some memory to array

You need to do 3 steps:

Step 1: Malloc the table node

node = (content*)malloc(sizeof(table));
node->rowsNumber = 5; // change to whatever you want

Step2: Malloc the array of pointers:

node->array = (char**)malloc(sizeof(char*)*(node->rowsNumber));

Step3: Malloc individual strings in array

for(i=0;i<node->rowsNumber,i++){
    node->array[i]=malloc(sizeof(char) * 8);// Change 8 to whatever size you want
}