Printing an array of structs in C - c

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)

Related

String in structure gets deleted

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;
}

Identify User Defined Function and Library Defined Function

I'm given a task to write a program that checks a piece of code, maximum of 20 lines of code, when the program runs you type in a function name, number of lines of code and type in the codes.
It's meant to search in the code and return if the function name you entered is a Library Function or User Defined Function or No Function if it doesn't find it, the code I've written is below, it doesn't work because I made mistakes and I've been trying to fix it but can't seem to figure it out, and I tried debugging to see where I made mistake, and I figured that in the function SearchRealisation it returns an error that
Run-Time Check Failure #2 - Stack around the variable 'buff' was
corrupted.
This program sample returns Library function instead of user defined function
type the function name: addition
Get count string in code: 9
int addition(int num1, int num2)
{
int result = num1 + num2; //trial
return result;
}
int main()
{
addition(8, 9);
}
Output is Library Function but correct output should be User Defined Function since it was defined in the code
void InputText(int length, char Text[MAX_STRINGS][MAX_COLUMNS])
{
//Repeat by Count String
gets_s(Text[0]);
for (int i = 0; i < length; i++)
gets_s(Text[i]);
//Output a string (starting with � zero and ending with Count String-1)
}
void OutMesseg(int param)
{
//Display one of three messages according to the parameter
if (param == -2)
printf("%s", "user defined function");
else if (param == -1)
printf("%s", "no function");
else
printf("%s", "library function");
}
char* DeleteComentsInString(char Text[MAX_STRINGS], char New[MAX_STRINGS])
{
char* a = strstr(Text, "//");
int len = strlen(Text);
if (a != NULL) len -= strlen(a);
strncpy(New, Text, len);
New[len] = '\0';
return New;
}
bool IsTypeC(char Word[MAX_STRINGS])
{
char ctype[6][MAX_STRINGS] =
{
"int",
"bool",
"char",
"float",
"double",
"void"
};
for (int i = 0; i < 6; i++)
{
if (strstr(Word, ctype[i]) != 0)
return true;
}
return false;
}
int SearchRealisation(int length, char Text[MAX_STRINGS][MAX_COLUMNS], int index_fanc, int& end)
{
int count = 0;
int start = -1;
end = -1;
char buff[MAX_STRINGS];
//Find first {
for (int i = index_fanc + 1; i < length && !count; i++)
{
if (strstr(DeleteComentsInString(Text[i], buff), "{") != NULL)
{
count++;
start = i;
}
}
//find last }
for (int i = start + 1; i < length && count; i++)
{
if (strstr(DeleteComentsInString(Text[i], buff), "{") != NULL)
count++;
else if (strstr(DeleteComentsInString(Text[i], buff), "}") != NULL)
count--;
if (!count)
end = i;
}
if (end == -1)
start = -1;
else
return start;
}
int SearchFunction(int length, char Text[MAX_STRINGS][MAX_COLUMNS], char FunctionName[MAX_COLUMNS], int& end)
{
//bool flag = false;
char commentDel[120];
int in;
for (int i = 0; i < length; ++i)
{
DeleteComentsInString(Text[i], commentDel);
if (strstr(commentDel, FunctionName) != NULL)
{
in = strlen(commentDel) - strlen(strstr(commentDel, FunctionName));
if ((in == 0 || (in != 0 && commentDel[in - 1] == ' ')) && (commentDel[in + strlen(FunctionName)] == ' ' || commentDel[in + strlen(FunctionName)] == '(') && strstr(commentDel, ";") == NULL)
{
return SearchRealisation(length, Text, i, end);
}
}
}
end = -1;
return -1;
}
int SearchResult(int length, char Text[MAX_STRINGS][MAX_COLUMNS], char FunctionName[MAX_COLUMNS])
{
int index;
int end;
int start = SearchFunction(length, Text, FunctionName, end);
if (start == -1)
return -1;
index = SearchFunction(length, Text, FunctionName, end);
if (index < 0)
return -2;
return index;
}
int findFunction(char string[MAX_STRINGS][MAX_COLUMNS], char* functName, int M)
{
return 0;
}
int main()
{
int length = 0;
char Code[MAX_STRINGS][MAX_COLUMNS] = { 0 };
char FunctionName[MAX_COLUMNS];
//char ConstantName[MAX_STRINGS];
printf("type the function name: ");
scanf("%s", &FunctionName);
printf("Get count string in code: ");
scanf("%d", &length);
InputText(length, Code);
printf("\n");
OutMesseg(SearchResult(length, Code, FunctionName));
return 0;
}
Well, you have been given a very difficult task:
There's no way to check this, as functions are resolved by a dynamic process that depends on your filesystem state, which is not available at runtime, after you have already compiled your program.
How do you distinguish a function that is compiled in a separate (but user defined) compilation unit from a system defined function? (e.g. double log(double);) that is defined in a math library? There is no way: the linker gets both from a different place (in the first case it gets it from the place you compiled the separate module, in the system case it gets it from a common library directory that has all the system related functions), but you don't have that information available at runtime).
In order to do this task feasible, you'd at least have the full set of source code files of your program. Preprocess them with the cpp(1) preprocessor (so you bypass all the macro expansion invocations) and then check for all function calls in the source code that are not provided in the full set of sources you have. This is quite similar to what the linker does. After compilation, the compiler leaves an object file with the compiled code, and a symbol table that identifies all the unresolved identifiers, and more important all the provided identifiers from this module. The linker then goes on all your modules trying to solve the unknowns, and for each that it doesn't have a solution in your code, it goes to the library directory to search for it. If it doesn't find it in either one, it fails telling you something is wrong.
In my opinion, you have been given a trap task, as the C language preprocess its input (this is something you should do, as many functions are hidden in the internals of macro bodies), then parse the code (for this, you need to write a C parser, which is no trivial task) to select which identifiers are defined in your code and which aren't. Finally you need to check all the calls you do in the code to divide the set in two groups, calls that are defined (and implemented) in your code, and calls that aren't (implemented, all the calls the compiler needs must be defined with some kind of prototype).
It's my opinion, but you have not a simple task, solvable in a short program (of perhaps one hundred lines) but a huge one.
Thanks a lot to everyone that answered I came up with a way to search the code for function definition and thereby return a value if its defined or not, or not even found, might not be the best solution to the task but works so far

C - scanf doesn't stop looping in string input

i'm making a small test to see if a word is inside another, and i want to return the index where that word begins.
Example: if i check "um" inside "amolum" the return value should be 4(position of the leter "u" where the word begins.
This is what my code looks like:
(...)
int cad_look_str (char s1[], char s2[]) {
int indS1 = 0, indS2 = 0;
while (s1[indS1]!='\0'|| s2[indS2]!='\0') {
if (s1[indS1]==s2[indS2]) {
indS1++;
indS2++;
}
else indS1=0;
}
if (s2[indS2]=='\0' && s1[indS1]!='\0') return -1;
else return indS2-strlen (s1);
}
void main () {
char s[100];
char s1[100];
scanf ("%s",s);
scanf ("%s",s1);
printf ("%d \n", cad_look_str(s1,s) );
}
The problem is that when i compile this, it doesn't stop looping on scanf... It just continues to ask for strings.
If i put cad_look_str(s1,s1) on the last line, it works fine... Why is this happening?
Regards
Your initial loop condition will never terminate if the first characters don't match your comparison test within your if statement.
The 'while' loop checks to ensure the current character positions (both 0 on first pass) are non-terminators. If they're not, and they're not equal, indS1 is reset to its starting position. indS2 never changes, thus the while condition is unchanged.
Might look at some other string functions to accomplish your task unless the scanning is a mandatory component for some reason.
Index of second string should be incremented in the else part also.
if (s1[indS1]==s2[indS2])
{
indS1++; indS2++;
}
else {
indS1=0;
indS2++;
}
changed cad_look_str() for situations like s1 : gdgddadada, s2 : dadada
int cad_look_str (char s1[], char s2[]) {
int indS1 = 0, indS2 = 0;
int flag = 0;
while (s1[indS1]!='\0'&& s2[indS2]!='\0') {
if (s1[indS1]==s2[indS2]) {
indS1++;
indS2++;
flag = 1;
}
else
{
indS1=0;
indS2++;
if(flag) indS2--; // to work with srtrings s1: gdgddadada s2: dadada
flag = 0;
}
}
if (s2[indS2]=='\0' && s1[indS1]!='\0') return -1;
else return indS2-strlen (s1);
}

User entered string run a particular function in c

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 !

Remove the duplicate from a String Using Pointers

#include<stdio.h>
char *removedps(char *x)
{
int Ar[256] = {0};
int ip=0;
int op=0;
char temp;
while(*(x+ip))
{
temp = (*(x+ip));
if (!Ar[temp]) {
Ar[temp] = 1;
*(x+ip) = *(x+op);
op++;
}
ip++;
*(x+op) = '\0';
}
return x;
}
int main()
{
char lo[] = "0001";
printf("%s",removedps(lo));
}
My code is not working
I have tried hard to see the error
All I GET IS the first character .
My idea is simple
make an array of 256 places
insert Zero into them
Then insert 1 for each character inside the string (on that position of the array)
your assignment looks to be the error here.
op is "out postiion", ip is "in position"
so it should be
*(x+op) = *(x+ip);
not the other way.
because *(x+op) = '\0';
is always run every iteration of the loop.
I'd probablly do it more like this ( using your method, which I probablly wouldn't use personally)
char *removedps(char *x)
{
int Ar[256] = {0};
char* start = x;
while(*x)
{
if (Ar[*x])
{ // remove the repeated character
memmove(x, x+1, strlen(x));
}
else
{
Ar[*x] = 1;
x++;
}
}
return start;
}
also, I'd name it remove_duplicate_chars or something, not a fan of cryptic abbreviations.
At the end of the loop, you do *(x+op)='\0';, and then, in the next iteration, you do *(x+ip)=*(x+op);, so from the 2sd iteration, you put there 0.
try do something like:
for (op=ip=0;x[ip];ip++) {
if (!Ar[x[ip]]++) x[op++]=x[ip];
}
x[op]=0;

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