I'm building a program that takes input as if it is a bare MAC address and turn it into a binary string. I'm doing this on a embedded system so there is no STD. I have been trying something similar to this question but after 2 days I haven't achieved anything, I'm really bad with these kind of things.
What I wanted is output to be equal to goal, take this into consideration:
#include <stdio.h>
int main() {
const char* goal = "\xaa\xbb\xcc\xdd\xee\xff";
printf("Goal: %s\n", goal);
char* input = "aabbccddeeff";
printf("Input: %s\n", input);
char* output = NULL;
// Magic code here
if (output == goal) {
printf("Did work! Yay!");
} else {
printf("Did not work, keep trying");
}
}
Thanks, this is for a personal project and I really want to finish it
First, your comparison should use strcmp else it'll be always wrong.
Then, I would read the string 2-char by 2-char and convert each "digit" to its value (0-15), then compose the result with shifting
#include <stdio.h>
#include <string.h>
// helper function to convert a char 0-9 or a-f to its decimal value (0-16)
// if something else is passed returns 0...
int a2v(char c)
{
if ((c>='0')&&(c<='9'))
{
return c-'0';
}
if ((c>='a')&&(c<='f'))
{
return c-'a'+10;
}
else return 0;
}
int main() {
const char* goal = "\xaa\xbb\xcc\xdd\xee\xff";
printf("Goal: %s\n", goal);
const char* input = "aabbccddeeff";
int i;
char output[strlen(input)/2 + 1];
char *ptr = output;
for (i=0;i<strlen(input);i+=2)
{
*ptr++ = (a2v(input[i])<<4) + a2v(input[i]);
}
*ptr = '\0';
printf("Goal: %s\n", output);
if (strcmp(output,goal)==0) {
printf("Did work! Yay!");
} else {
printf("Did not work, keep trying");
}
}
Related
I'm working on the last exercise of the "Think like a computer scientist, C version" book and I have some trouble with one particular point.
The exercise consists of making a small game, where the computer picks a random value between 0 and 20 and then asks me to guess the number.
After that, the computer counts the number of tries I made and, if I get a better score than the previous party, I need to store my name and the number of tries in a structure.
My problem is the following: When I restart the game, the string value, player_name, in the structure gets somehow deleted but player_score is still there.
First, I made a "call by value" function to create the structure and then a tried with a "call by reference" but getting the same results.
I think I tried everything I could with my actual knowledge for now; so, if someone could check my code and give me some tips about what's wrong I would much appreciate it!
//HEADERS
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define FALSE 0
#define TRUE 1
//TYPEDEF STRUCTS
typedef struct
{
int player_score;
char *player_name;
} HS_Player;
//FUNCTION PROTOTYPES
int Random_Value(void);
int Get_User_Choice(void);
int Check_Result(int computer, int my_choice);
int Try_Again(int game_result, int computer);
void Player_Infos(HS_Player *player_p, int score);
int Game_Restart(void);
//MAIN
int main(void)
{
int end_game;
int high_score_value = 100;
HS_Player player;
while (end_game != TRUE)
{
int computer_number = Random_Value();
printf("Guess the number between 0 et 20 chosen by the computer.\n");
int your_number = Get_User_Choice();
int result_game = Check_Result(computer_number, your_number);
int tries_to_win = Try_Again(result_game, computer_number);
printf("Number of tries: %i\n", tries_to_win);
if (tries_to_win < high_score_value)
{
Player_Infos(&player, tries_to_win );
high_score_value = player.player_score;
}
printf("Highest score: %i By: %s\n", player.player_score, player.player_name);
printf("\n");
end_game = Game_Restart();
}
return EXIT_SUCCESS;
}
//Random_Value FUNCTION
int Random_Value(void)
{
srand(time(NULL));
int x = rand();
int y = x % 20;
return y;
}
//Get_User_Choice FUNCTION
int Get_User_Choice(void)
{
int success, x;
char ch;
printf("Your Guess:\t");
success = scanf("%i", &x);
while (success != 1)
{
printf("Your input is not a number. Please try again:\t");
while ((ch = getchar()) != '\n' && ch != EOF);
success = scanf("%i", &x);
}
if (x < 0 || x > 20)
{
printf("Your input must be between 0 and 20. Please try again.\n");
Get_User_Choice();
}
return x;
}
//Check_Result FUNCTION
int Check_Result(int computer, int my_choice)
{
int check_result;
if (my_choice < computer)
{
printf("Computer number is larger!\n");
check_result = FALSE;
}
else if (my_choice > computer)
{
printf("Computer number is smaller!\n");
check_result = FALSE;
}
else if (my_choice == computer)
{
printf("It's a Match! You chose the same number than the computer.\n");
printf("\n");
check_result = TRUE;
}
return check_result;
}
//Try_Again FUNCTION
int Try_Again(int game_result, int computer)
{
int tries_befor_success = 1;
while (game_result != TRUE)
{
int your_number = Get_User_Choice();
game_result = Check_Result(computer, your_number);
tries_befor_success++;
}
return tries_befor_success;
}
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
player_p->player_name = new_name;
}
//Game_Restart FUNCTION
int Game_Restart(void)
{
int quit_value;
printf("Quit Game ?\n");
printf("Press 'y' to quit or any other keys to continue.\n");
fflush(stdin);
char quit_game = getchar();
printf("\n");
if (quit_game == 'y')
{
quit_value = TRUE;
}
else
{
quit_value = FALSE;
}
return quit_value;
}
The problem is that, in your Player_Infos function, you are assigning the address of a local array to the char* player_name pointer member of the passed structure. When that function ends, the local array it used will be deleted and the pointer in the structure will be invalid. (In the case of the player_score, you don't have that problem, because the given value is copied to the structure member.)
There are several ways around this; one would be to use the strdup() function to make a copy of the local char new_name[80]; array – but that is really overkill, and you would need to manage (i.e. free()) that allocated string whenever you make a modification.
A simpler way is to make the player_name member an actual array of char and then use strcpy() to copy the local array into that member.
Better, still, with the player_name member defined as char [80], you can read directly into that (in the function), and avoid the local array completely:
typedef struct
{
int player_score;
char player_name[80];
} HS_Player;
//...
void Player_Infos(HS_Player *player_p, int score)
{
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
// Read directly. Limit input to 79 chars (allowing room for null terminator).
scanf("%79s", player_p->player_name);
printf("\n");
player_p->player_score = score;
}
Also, just as a "style" tip, you may want to change the member names to just score and name, as the "player" part is implied by the structure type-name itself.
This issue you are having is that you are associating the player name pointer to a variable that goes out of scope when you leave the "player_Infos" function. What you probably would want to do is define the name as a character array in your structure and then use the "strcpy" call in your function instead. Following is a couple of code snippets illustrating that point.
//TYPEDEF STRUCTS
typedef struct
{
int player_score;
char player_name[80];
} HS_Player;
Then, in your function, use the "strcpy" call.
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
strcpy(player_p->player_name, new_name);
//player_p->player_name = new_name;
}
When I tested that out, I got a name to appear in the terminal output.
Computer number is smaller!
Your Guess: 4
It's a Match! You chose the same number than the computer.
Number of tries: 8
Highest score: 4 By: Craig
FYI, you will need to include the "string.h" file.
Give that a try.
Name Update
The reason your player.player_name is not getting updated is because you can't assign a string this way in C. When doing player_p->player_name = new_name; you're actually saving in player_p->player_name the memory address of new_name.
Instead, what you want to achieve, is to copy each character of new_name to player_p->player_name and in order to achieve this, you have to change the type of prlayer_name field from char* player_name to char player_name[80], then assign it using, for example, strcpy():
#include <string.h>
// [...]
//TYPEDEF STRUCTS
typedef struct
{
unsigned int player_score;
char player_name[80];
} HS_Player;
// [...]
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
strcpy(player_p->player_name, new_name);
}
Data Persistence
To make data (players info) persistent over multiple runs, you have to save the content of the struct to a file.
Example
int Save_Score(char* filename, HS_Player* player)
{
FILE* file = fopen(filename, "w");
if (file == NULL)
{
fprintf(stderr, "\nAn error occurred while opening the file\n");
return -1;
}
if (fprintf(file, "%d %s", player->player_score, player->player_name) < 0)
return -1;
fclose(file);
return 0;
}
int Load_Score(char* filename, HS_Player* player)
{
FILE* file = fopen(filename, "r");
if (file == NULL)
{
fprintf(stderr, "\nAn error occurred while opening the file\n");
return -1;
}
if (fscanf(file, "%d %79s", &player->player_score, player->player_name) < 0)
return -1;
fclose(file);
return 0;
}
#include <stdio.h>
int limit;
char alp[26]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','w','x','y','z'};
void encode(char message[21],char enc_message[21],int key);
void decode(char enc_message[21],char dec_message[21],int key);
main()
{
int key,i=0,j=0;
char message[21];
char enc_message[21];
char dec_message[21];
char encrypted[21];
char a='\0';
printf("Input the characters to encrypt\n");
while(i<21 && a!='\n')
{
scanf("%c",&a);
message[i]=a;
i=i+1;
}
for(i=0;;i++) /*custom strlen*/
{
if( message[i]= '\0')
{
limit=i;
break;
}
}
printf("Input the key");
scanf("%d",key);
for(i=0;i<21;i++)
{
enc_message[i]=message[i];
}
encode(message[21],enc_message[21],key);
for(i=0;i<21;i++)
{
dec_message[i]=enc_message[i];
}
for(i=0;i<limit;i++)
{
printf("%c",enc_message[i]);
}
printf("\n\n");
decode(enc_message[21],dec_message[21],key);
for(i=0;i<limit;i++)
{
printf("%c",dec_message[i]);
}
}
void encode(char message[21],char enc_message[21],int key)
{
/*char temp[21];*/
int x,y;
for(x=0;x<limit;x++) /* message check */
{
for(y=0;y<26;y++) /* <----- alphabet check */
{
if (enc_message[x]==alp[y]) enc_message[x]=alp[y+key];
}
}
}
/*------------------------------------------------------------------------*/
void decode(char enc_message[21],char dec_message[21],int key)
{
int x,y;
for (x=0;x<limit;x++)
{
for(y=0;y<26;y++)
{
if (dec_message[x]==alp[y+key]) dec_message[x]=alp[y];
}
}
}
The compiler says,the mistake has to do with the way I call functions(and write them)and says: passing argument1 of 'encode' makes pointer from integer without a cast ,and that is for argument 2 of 'encode' and the exact same for 'decode'
Thanks in advance!
You are passing a single element and it's not even a valid element, try
decode(enc_message, dec_message, key);
Also, format your code so it's readable that is really important, and looping to compute the length of the string to use it in another loop is not a very smart thing, print it in a loop like
for (int i = 0 ; enc_message[i] != '\0' ; ++i) ...
also, don't over use break, just think about the logical condition for the loop, it's the same one where you break. Code is much more readable if the condition appears in the right place.
I'm trying to print an array of structs that contain two strings. However my print function does not print more than two indices of the array. I am not sure why because it seems to me that the logic is correct.
This is the main function
const int MAX_LENGTH = 1024;
typedef struct song
{
char songName[MAX_LENGTH];
char artist[MAX_LENGTH];
} Song;
void getStringFromUserInput(char s[], int maxStrLength);
void printMusicLibrary(Song library[], int librarySize);
void printMusicLibraryTitle(void);
void printMusicLibrary (Song library[], int librarySize);
void printMusicLibraryEmpty(void);
int main(void) {
// Announce the start of the program
printf("%s", "Personal Music Library.\n\n");
printf("%s", "Commands are I (insert), S (sort by artist),\n"
"P (print), Q (quit).\n");
char response;
char input[MAX_LENGTH + 1];
int index = 0;
do {
printf("\nCommand?: ");
getStringFromUserInput(input, MAX_LENGTH);
// Response is the first character entered by user.
// Convert to uppercase to simplify later comparisons.
response = toupper(input[0]);
const int MAX_LIBRARY_SIZE = 100;
Song Library[MAX_LIBRARY_SIZE];
if (response == 'I') {
printf("Song name: ");
getStringFromUserInput(Library[index].songName, MAX_LENGTH);
printf("Artist: ");
getStringFromUserInput(Library[index].artist, MAX_LENGTH);
index++;
}
else if (response == 'P') {
// Print the music library.
int firstIndex = 0;
if (Library[firstIndex].songName[firstIndex] == '\0') {
printMusicLibraryEmpty();
} else {
printMusicLibraryTitle();
printMusicLibrary(Library, MAX_LIBRARY_SIZE);
}
This is my printing the library function
// This function will print the music library
void printMusicLibrary (Song library[], int librarySize) {
printf("\n");
bool empty = true;
for (int i = 0; (i < librarySize) && (!empty); i ++) {
empty = false;
if (library[i].songName[i] != '\0') {
printf("%s\n", library[i].songName);
printf("%s\n", library[i].artist);
printf("\n");
} else {
empty = true;
}
}
}
I think the problem is caused due to setting : empty = true outside the for loop and then checking (!empty) which will evaluate to false. What I am surprised by is how is it printing even two indices. You should set empty = false as you are already checking for the first index before the function call.
The logic has two ways to terminate the listing: 1) if the number of entries is reached, or 2) if any entry is empty.
I expect the second condition is stopping the listing before you expect. Probably the array wasn't built as expected (I didn't look at that part), or something is overwriting an early or middle entry.
you gave the definition as:
typedef struct song
{
char songName[MAX_LENGTH];
char artist[MAX_LENGTH];
}Song;
the later, you write if (library[i].songName[i] != '\0') which really seems strange: why would you index the songname string with the same index that the lib?
so I would naturally expect your print function to be:
// This function will print the music library
void printMusicLibrary (Song library[], int librarySize) {
for (int i = 0; i < librarySize; i ++) {
printf("%s\n%s\n\n", library[i].songName,
library[i].artist);
}
}
note that you may skip empty song names by testing library[i].songName[0] != '\0' (pay attention to the 0), but I think it would be better not to add them in the list (does an empty song name make sens?)
(If you decide to fix that, note that you have an other fishy place: if (Library[firstIndex].songName[firstIndex] == '\0') with the same pattern)
Guys so I'm working on the web service assignment and I have the server dishing out random stuff and reading the uri but now i want to have the server run a different function depending on what it reads in the uri. I understand that we can do this with function pointers but i'm not exactly sure how to read char* and assign it to a function pointer and have it invoke that function.
Example of what I'm trying to do: http://pastebin.com/FadCVH0h
I could use a switch statement i believe but wondering if there's a better way.
For such a thing, you will need a table that maps char * strings to function pointers. The program segfaults when you assign a function pointer to string because technically, a function pointer is not a string.
Note: the following program is for demonstration purpose only. No bounds checking is involved, and it contains hard-coded values and magic numbers
Now:
void print1()
{
printf("here");
}
void print2()
{
printf("Hello world");
}
struct Table {
char ptr[100];
void (*funcptr)(void)
}table[100] = {
{"here", print1},
{"hw", helloWorld}
};
int main(int argc, char *argv[])
{
int i = 0;
for(i = 0; i < 2; i++){
if(!strcmp(argv[1],table[i].ptr) { table[i].funcptr(); return 0;}
}
return 0;
}
I'm gonna give you a quite simple example, that I think, is useful to understand how good can be functions pointers in C. (If for example you would like to make a shell)
For example if you had a struct like this:
typedef struct s_function_pointer
{
char* cmp_string;
int (*function)(char* line);
} t_function_pointer;
Then, you could set up a t_function_pointer array which you'll browse:
int ls_function(char* line)
{
// do whatever you want with your ls function to parse line
return 0;
}
int echo_function(char* line)
{
// do whatever you want with your echo function to parse line
return 0;
}
void treat_input(t_function_pointer* functions, char* line)
{
int counter;
int builtin_size;
builtin_size = 0;
counter = 0;
while (functions[counter].cmp_string != NULL)
{
builtin_size = strlen(functions[counter].cmp_string);
if (strncmp(functions[counter].cmp_string, line, builtin_size) == 0)
{
if (functions[counter].function(line + builtin_size) < 0)
printf("An error has occured\n");
}
counter = counter + 1;
}
}
int main(void)
{
t_function_pointer functions[] = {{"ls", &ls_function},
{"echo", &echo_function},
{NULL, NULL}};
// Of course i'm not gonna do the input treatment part, but just guess it was here, and you'd call treat_input with each line you receive.
treat_input(functions, "ls -laR");
treat_input(functions, "echo helloworld");
return 0;
}
Hope this helps !
I have a definite set of strings and its corresponding numbers:
kill -> 1
live -> 2
half_kill -> 3
dont_live -> 4
List is of 30 such strings and their number mapping.
If user enters "kill", I need to return 1 and if he enters "dont_live" I need to return 4.
How should I achieve this in c program? I am looking for an efficient solution because this operation needs to be done 100s of times.
should I put them in #define in my .h file?
Thanks in advance.
Sort your table, and use the standard library function bsearch to perform a binary search.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct entry {
char *str;
int n;
};
/* sorted according to str */
struct entry dict[] = {
"dont_live", 4,
"half_kill", 3,
"kill", 1,
"live", 2,
};
int compare(const void *s1, const void *s2)
{
const struct entry *e1 = s1;
const struct entry *e2 = s2;
return strcmp(e1->str, e2->str);
}
int
main (int argc, char *argv[])
{
struct entry *result, key = {argv[1]};
result = bsearch(&key, dict, sizeof(dict)/sizeof(dict[0]),
sizeof dict[0], compare);
if (result)
printf("%d\n", result->n);
return 0;
}
Here's what you get when you run the program.
$ ./a.out kill
1
$ ./a.out half_kill
3
$ ./a.out foo
<no output>
PS: I reused portions of sidyll's program. My answer should now be CC BY-SA compliant :p
A possible solution:
#include <stdio.h>
#include <string.h>
struct entry {
char *str;
int n;
};
struct entry dict[] = {
"kill", 1,
"live", 2,
"half_kill", 3,
"dont_live", 4,
0,0
};
int
number_for_key(char *key)
{
int i = 0;
char *name = dict[i].str;
while (name) {
if (strcmp(name, key) == 0)
return dict[i].n;
name = dict[++i].str;
}
return 0;
}
int
main (int argc, char *argv[])
{
printf("enter your keyword: ");
char s[100]; scanf("%s", s);
printf("the number is: %d\n", number_for_key(s));
return 0;
}
Here's one approach:
int get_index(char *s)
{
static const char mapping[] = "\1.kill\2.live\3.half_kill\4.dont_live";
char buf[sizeof mapping];
const char *p;
snprintf(buf, sizeof buf, ".%s", s);
p = strstr(mapping, buf);
return p ? p[-1] : 0;
}
The . mess is to work around kill being a substring of half_kill. Without that issue you could simply search for the string directly.
If it is a very short list of strings then a simple block of ifs will be more than sufficient
if (0 == strcmp(value, "kill")) {
return 1;
}
if (0 == strcmp(value, "live")) {
return 2;
}
...
If the number approach 10 I would begin to profile my application though and consider a map style structure.
if you have a fixed set of strimgs, you have two options: generate a perfect hashing function (check gperf or cmph) or create a trie so that you never have to check charcters more than once.
Compilers usually use perfect hashes to recognize a language keyword, in your case I would probably go with the trie, it should be the fastest way (but nothing beats direct measurement!)
Is it really a bottleneck? You should worry about efficiency only if the simple solution proves to be too slow.
Having said that, possible speed improvements are checking the lengths first:
If it's 4 characters then it could be "kill" or "live"
If it's 9 characters then it could be "half_kill" or "dont_live"
or checking the first character in a switch statement:
switch (string[0]) {
case 'k':
if (strcmp(string, "kill") == 0)
return 1;
return 0;
case 'l':
...
default:
return 0;
}
Use hashmap/ hashtable i think this would be the best solution.
Can you use an Enumunerator?
int main(void) {
enum outcome { kill=1, live, half_kill, dont_live };
printf("%i\n", kill); //1
printf("%i\n", dont_live); //4
printf("%i\n", half_kill); //3
printf("%i\n", live); //2
return 0;
}
Create a list of const values:
const int kill = 1;
const int live = 2;
const int half_kill = 3;
etc