从关联指针数组中按字符读取字符串char

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I create a new char *ch malloc(strlen) and loop that string char by char. Then i copy it back using memcpy(ch, &stringpool[index], len) Of course, afterwards free(ch) .

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I hope the title of my question is correct.

I have a stringpool

char **string_pool;

that gets initiated in a function like

string_pool = malloc( sizeof(char *) * 1024);

i get strings from stdin and scanf them into the array

scanf("%[^\n]s", &string_pool[index]);

so i can print it out using printf

printf("gets %s\n", &string_pool[index]);

how can i

• get the length of string_pool[index]
• read string_pool[index] char by char in a loop

Thank you

Edit

Maybe i should explain it a bit more, its a virtual machine with a virtual instruction set and a program like

push 1
read
gets

should :

• push 1 on the stack -> let x be 1
• read stdin as string into string_pool[x]
• push all characters onto the stack

the functions looks like

    case GETS: {
        int index = popv(); // index is already on top of the stack
        int strl = strlen(&string_pool[index]);

        printf("gets %s with a length of %d\n", &string_pool[index], strl);
        // pseudo code
        // push each char as integer on the stack
        foreach(char in string_pool[index]) push((int)char);

        break;
    }

    case READ: {  
        int index = popv();          
        scanf("%[^\n]s", &string_pool[index]);
        break;
    }

    case WRITE: {  
        int index = popv();          
        printf("%s", &string_pool[index]);
        break;
    }

My problem is in the GETS case. I want to push every char as int onto the stack.

Answer 1

 char **string_pool; string_pool = malloc( sizeof(char *) * 1024); 

Allocates 1024 pointers-to-char . ( string_pool is a pointer-to-pointer-to-char ) Each of the pointers are uninitialized and point to no valid storage that can be used. Before you can use each pointer, you must make them point to valid memory by allocating memory and assigning the starting address to each pointer (so that each pointer "points" to valid memory).

To allow proper sizing and allocation for each string your read, you will either use fgets with a fixed buffer sufficient to store the longest input you expect, or you can use POSIX getline which will allocate storage for input as required. Using fgets you would do something similar to:

#define MAXCHR 2048
...

char buffer[MAXCHR];

fputs ("enter string: ", stdout);
if (fgets (buffer, MAXCHR, stdin) == NULL) {
    fputs ("(user canceled input.)\n", stderr);
    return 1;
}

size_t len = strlen (buffer);   /* get the length of input (with '\n') */
if (len && buffer[len - 1] == '\n')    /* trim the '\n' from end */
    buffer[--len] = 0;          /* by overwriting with nul-character */


string_pool[index] = malloc (len + 1);      /* allocate storage for buffer */
if (string_pool[index] == NULL) {           /* validate allocation */
    perror ("maklloc-string_pool[index]");  /* handle error */
    return 1;  /* or break read loop; */
}
/* copy buffer to string_pool[index], advance index */
memcpy (string_pool[index++], buffer, len + 1); 

You would generally do this within your read loop only allowing input while index < 1024 to insure you did not attempt to allocate storage for one pointer too many.

Look things over and let me know if you have questions.

Answer 2

You must allocate space for each string. So, for example,

string_pool[0] = malloc( 100 );

will then allow you to read a string that is up to 99 characters long into string_pool[0] (the extra space is needed for the terminating null).