我只是想将字符串扫描到数组中。 我究竟做错了什么？

Question

#include <stdio.h>
#include <string.h>

int main(void) {

   const int NUM_VALS = 20;
   int i;
   int actualInput;
   char userString[actualInput][NUM_VALS];
   int matchCount = 0;

   scanf("%d", &actualInput);

   for (i = 0; i < actualInput; ++i) {
      scanf("%s", userString[i]);
      printf("%s", userString[i]);
   }



   return 0;
}

Output:

b'hellohi\\x80\\x07@\\xd2\\x05@\\x9a\\x16[\\xea\\xccp\\xa6\\x15\\xf6\\x18+\\xbf\\x87\\x8a#\\x14)\\x05@\\xfe\\x7f'b'\\x92\\x1fk\\xb3\\xfe\\x7f\\xfe\\x7f\\x118\\x08\\xe8\\x03\\x0eY\\x03k\\xb3\\xfe\\x7f\\xfe\\x7f\\xb2Y{\\xe8C}8\\r\\x8b-u{\\x8cx86_64'F-8sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin/usr/sbin:/usr/bin:/sbin:/binsbin:/binTF-88tf8RELOAD=/usr/lib/x86_64-linux-gnu/coreutils/libstdbuf.so64-linux-gnu/coreutils/libstdbuf.sols/libstdbuf.soout

I've tried some variations replacing userString[i] with userString in the scanf function. The result is outputting 50,000 inputs of my last string. I don't understand what's happening.

Answer 1

The problem is this sequence of code:

int actualInput;
char userString[actualInput][NUM_VALS];
int matchCount = 0; 

scanf("%d", &actualInput);

The first line declares a variable called actualInput but doesn't assign a value to that variable.

The second line declares a variable length array (VLA) using the value in actualInput . Using the value of an uninitialized variable results in undefined behavior , which basically means that after that point in the code, anything can happen. What's likely happening (based on your description of the problem) is that actualInput is either zero, or a small number, so you get an array that's too small to hold your input.

The last line (with the scanf ) finally assigns a value to actualInput . You may be thinking that the array will resize itself when actualInput is changed. That definitely does not happen. In C, after a VLA is created, its size cannot be changed.

The solution is simple, rearrange the code so that things are done in the proper order:

int actualInput;
scanf("%d", &actualInput);
char userString[actualInput][NUM_VALS];

int matchCount = 0;

As a side note, you should really do some error checking to make sure that the user inputs a reasonable number, before using that number to create an array. For example

int actualInput;
if (scanf("%d", &actualInput) != 1 || actualInput < 1 || actualInput > 1000)
{
    printf("That is not a valid array size\n");
    return 1;
}
char userString[actualInput][NUM_VALS];

Answer 2

you cant declare it as a 2D array then treat it as a normal array . each case should include only one letter but it can't be done automatically , I suggest you add this :

for (i = 0; i < actualInput; ++i) 
{
    gets(stri);
    for (k=0;k<strlen(stri);k++)
    userString[i][j]=stri[j];
}