结构中的 printf 字符数组也在 C 中打印下一个 int

Question

I am very new to C and I don't know that much about it, although I do have some experience with programming as a whole. Whenever I get warnings or errors I just look it up online. But this one doesn't give a warning or an error. It runs fine but it gives the wrong result.

So I have a structure with a char[16] and 2 ints:

struct tile {
char layout[16];
int arrowClr;
int spPlacing;
};

I make an array of 200 of them with struct tile tiles[200]; . Then I open a file with a list of characters & numbers:

char resourceName[5];
scanf("%s",&*resourceName);

char rLoc[100];
sprintf(rLoc,"Resources/%s/",resourceName);

char tileLoc[100];
sprintf(tileLoc,"%sTiles.txt",rLoc);
FILE *tile_list;
tile_list = fopen(tileLoc,"r");

This is the list:

   w s d   d   w20
wwwww   w s w  w10
w  wws ww  ww  w10
w  ww  ww sww  w10
   w  sw   w   w20
ws ww  ww  ww  w21
wwww     w  w  w10
ws  w   w   w   20
wwwww   w  sw   20
w  ww  dws dw  w10
wwww  s         20
w  ww sww  ww  w11
wwww   w s w   w20
wddw  sw   w   w10
wwww    s       20
w  wd swd  ww  w20
w  w  s     w  w20
wddww   w s w   20
wddww sww  ww  w20
w  ww  wws ww  w10
wwww   w   ww  w10

After that, I cycle through each line, storing the 16 first characters in the structure layout char (I used sprintf to make it know it was a character, because otherwise it just gave ascii value) and the last two numbers in the two ints:

for (int i=0;fgets(buf,100,tile_list)!=NULL;i++) {
strtok(buf,"\n");
//printf("%s",buf);
//printf("%c\n",buf[0]);
for (int e=0;e<16;e++) {
    sprintf(&tiles[i].layout[e],"%c",buf[e]);
}
tiles[i].arrowClr = buf[16];
tiles[i].spPlacing = buf[17];
}

Then, I display each of them to test it (without the two ints) with:

for (int i=0;i<21;i++) {
printf("%s\n",tiles[i].layout);
}

And this is the result:

   w s d   d   w2
wwwww   w s w  w1
w  wws ww  ww  w1
w  ww  ww sww  w1
   w  sw   w   w2
ws ww  ww  ww  w2
wwww     w  w  w1
ws  w   w   w   2
wwwww   w  sw   2
w  ww  dws dw  w1
wwww  s         2
w  ww sww  ww  w1
wwww   w s w   w2
wddw  sw   w   w1
wwww    s       2
w  wd swd  ww  w2
w  w  s     w  w2
wddww   w s w   2
wddww sww  ww  w2
w  ww  wws ww  w1
wwww   w   ww  w1

Removing the tiles[i].arrowClr = buf[16]; makes that last number disappear from each line, and making the for loop before it go while e<15 instead of e<16 makes it disappear too, also making the last character before it vanish too.

BTW I know tiles[i].arrowClr = buf[16]; & tiles[i].spPlacing = buf[17]; give me the ascii values of the numbers, that's just another problem, if anybody knows how to fix that too that would be useful

Answer 1

1. You are not null terminating the layout string. If this string is has 16 characters, add one to the layout array for the null. layout[16] = '\\0'
2. You need to convert ASCII strings to numbers if that is your intent. arrowClr = buf[16] - '0';

Answer 2

In this line

printf("%s\n",tiles[i].layout);

there is expected to be a string terminator '\\0' at the end of the string. But you didn't put one. You built the string like this

for (int e=0;e<16;e++) {
    sprintf(&tiles[i].layout[e],"%c",buf[e]);
    ...

Your struct definition needs an extra char length

char layout[17];        // <--- 16 to 17

and then after copying chars from the file, you need

tiles[i].layout[16] = '\0';

to terminate the string so you can print it.

Then, the last two fields which you obtain with

tiles[i].arrowClr = buf[16];
tiles[i].spPlacing = buf[17];

should be like this, to convert the single digit ASCII value to an int type

tiles[i].arrowClr = buf[16] - '0';
tiles[i].spPlacing = buf[17] - '0';

asuming that you intended the read value to be the number 1 or 2 and not the character '1' or '2' .

Answer 3

As I and others mentioned, you need to allocate at least one more byte to your string. But I would also recommend replacing your for loop (%c) with a simple call to snprintf() . That will let you specify the 16 bytes you want from buf .

Answer 4

You need a nul character ( '\\0' ) at the end of your string if you want to use it with standard C string functions.

Arrays in C don't have any length information associated with them, so in order for printf to know when it's reached the end of a string it needs some sort of marker. The nul character is used for this (also by all other string related functions like strlen , strcpy , etc.).

Answer 5

You're using the layout field as an array of characters, but you're trying to print it as a string. In C a string is a NULL terminated array of characters. Since your array doesn't have a NULL terminator, printf keeps looking until it finds a 0 byte, which it ends up finding in the arrowClr field which is laid out next in memory. That's why it's printing out the number.

You need to either make layout one character bigger, ie char layout[17] , and set layout[16] = 0 , or you would need to run printf in a loop to print each character individually. I'd recommend the former.

To get the numerical values of the last two characters, you need to do this:

tiles[i].arrowClr = buf[16] - '0';
tiles[i].spPlacing = buf[17] - '0';