Thread: Structures on functions

I need to use structure variables on a function but when compiling, get an error.
I need to create a function (homework) to compare different data from a structure.

Code:

//Structure definition

typedef struct {
    char text1[5], text2[5];
    int val1, val2;
    boolean hasSome;
}tCar;

//tCar variable declaration
tCar car1, car2;

now I need to compare all structure variables using a function to return the following value considering next requirements (strings comparsion is made depending of the initial character in alphabetic order):

if car1> car2 = 1 //if a parameter of car1 is bigger than car1, return 1
if car2> car1 = -1 //if a parameter of car2 is bigger than car1, return -1
if car1 = car2 = 0 //if all compared variables are equal, the function returns 0

So could you help in order to create a function that compare all the parameters returning a value for each case?
(I'm really new with C, just some days ago programming).

I'm not sure about the function header and body...

I've tried:

Code:

//header
int car_cmp (tCar car1, tCar car2) { //but got an error of undefined tCar

About the body, I understand I should use strcmp function for strings comparison (for all other variables no problem), but not sure of how to use it...perhaps:

Code:

int text_cmp;
int result;
text_cmp = strcmp(text1, text2);
if (text_cmp > 0) {
result = 1;
if (text_cmp < 0) {
result = -1;
if (text_cmp) ==0){
result = 0;

//function return
}return result;

Is this right?

I just paste the code I have now (just one comparison):

Code:

//System header files
#include <stdio.h>
#include <string.h>


//constants
int const MAX_CHAR = 10;


//function Header
int car_cmp(tCar car1, tCar car2);


//Main function
int main(int argc, char* argv[]) {
	typedef struct{
	  char carBrand[MAX_CHAR];
	  char carModel[MAX_CHAR];
	}tCar;
	tCar car1, car2;
	printf("Introduce car1 Brand Text: ");
	scanf("%s", car1.carBrand);
	printf("Introduce car2 Brand Text: ");
	scanf("%s", car2.carBrand);
  	printf("Introduce car1 Model Text: ");
	scanf("%s", car1.carModel);
	printf("Introduce car2 Model Text: ");
	scanf("%s", car2.carModel);
	
	printf("the result of comparing the two cars is: %d", car_cmp(result)); //function call


   return 0;
}


int car_cmp(tCar car1, tCar car2){
	int text_cmp;
	int result;
	text_cmp = strcmp(car1.carBrand, car2.carBrand);
	if (text_cmp>0){
		result = 1;
	}
}return result;

And now got these errors / warnings:

Code:

/*error: unknown type name 'tCar'; did you mean 'char'?

Code:

 int car_cmp(tCar car1, tCar car2);
             ^~~~
             char
 error: unknown type name 'tCar'; did you mean 'char'?
 int car_cmp(tCar car1, tCar car2);
                        ^~~~
                        char
 warning: implicit declaration of function 'car_cmp'; did you mean 'strncmp'? [-Wimplicit-function-declaration]
  printf("the result of comparing the two cars is: %d", car_cmp(result));
                                                        ^~~~~~~
                                                        strncmp
 error: 'result' undeclared (first use in this function)
  printf("the result of comparing the two cars is: %d", car_cmp(result));
                                                                ^~~~~~
 error: unknown type name 'tCar'; did you mean 'char'?
 int car_cmp(tCar car1, tCar car2){
             ^~~~
             char
error: unknown type name 'tCar'; did you mean 'char'?
 int car_cmp(tCar car1, tCar car2){
                        ^~~~
                        char
 error: expected identifier or '(' before 'return'
 }return result;


====6 errors, 2 warnings====*/

but there's a car_cmp header before, telling to main that car_cmp function exists. Is not the puropose of a header declaration? if not, could you please show me an example?

Originally Posted by Akeold

but there's a car_cmp header before, telling to main that car_cmp function exists. Is not the puropose of a header declaration? if not, could you please show me an example?

That tells it that the function exists. It does not tell it what a tCar is. You have to tell it what a tCar is before you can use it. In fact your function doesn't know what a tCar is either, because that definition is hidden in main and is only accessible inside main, and therefore not available to the function.

Originally Posted by laserlight

Kernelpanic: gets is inherently vulnerable to buffer overflow. You must never use it. Consider alternatives like fgets and scanf with %s and a field width instead.

@laserlight - I know, but I am a bad boy. Yeah that's right! The input with 'gets' is more simple. In the next version fgets and sscanf like so - below Moeglichkeit 3:
Rheinwerk Computing :: C von A bis Z – 4 Formatierte Ein-/Ausgabe mit »scanf()« und »printf()«

Also, note that fflush(stdin) technically results in undefined behaviour. Look into a loop to read and discard characters until the first new line character instead.

Yes, fflush is for rest of input like '\n' and also simple.
Ok, thanks for your tips.

I use the programming in C as relaxtion and for diversion - or so.
Have a nice weekend.

Originally Posted by Kernelpanic

//Allacation of the adresses of both structures
//Zuweisung der Adressen der beiden Strukturen
zgr_w1 = &wagen1;
zgr_w2 = &wagen2;

It is an allocation of the address of the structure with two variables. Sorry.

Originally Posted by laserlight

Kernelpanic: gets is inherently vulnerable to buffer overflow. You must never use it. Consider alternatives like fgets and scanf with %s and a field width instead.

Also, note that fflush(stdin) technically results in undefined behaviour. Look into a loop to read and discard characters until the first new line character instead.

With fgets it is well, "scanf" with %s and a field width I still don't understand. Instead of fflush(stdin) now with getchar() but in the output the text line will wrap.

Code:

//Daten einlesen - Input data
    printf("\nFirma    : ");
    fgets(wagen1.firma, MAX, stdin);
    printf("Modell   : ");
    fgets(wagen1.modell, MAX, stdin);
    
    printf("Anzahl PS: ");        
    do {scanf("%f", &wagen1.ps);} while(getchar() != '\n' && getchar() != EOF);
        printf("Preis    : ");    
    do {scanf("%f", &wagen1.preis);} while(getchar() != '\n' && getchar() != EOF);
        
    printf("\nFirma    : ");
    fgets(wagen2.firma, MAX, stdin);
    printf("Modell   : ");
    fgets(wagen2.modell, MAX, stdin);
    
    printf("Anzahl PS: ");
    do {scanf("%f", &wagen2.ps);} while(getchar() != '\n' && getchar() != EOF);    
    printf("Preis    : ");
    do {scanf("%f", &wagen1.preis);} while(getchar() != '\n' && getchar() != EOF);

And this loop works once only.

Code:

//Daten einlesen
    printf("\nFirma    : ");
    fgets(wagen1.firma, MAX, stdin);
        
    printf("Modell   : ");
    fgets(wagen1.modell, MAX, stdin);
    
    printf("Anzahl PS: ");
    scanf("%f", &wagen1.ps);


    printf("Preis    : ");
    scanf("%f", &wagen1.preis);
    
    int c;
    do    
        c = getchar();
    while(c != '\n' && c != EOF);

With loop:


Line wrap:

Note that fgets keeps the new-line character, which means it is your responsibility to remove it.

%s won't allow for input with spaces in it, so if you wanted that (and it looks like you do!) you would need to use a scanset instead (again with a length given).

Code:

scanf("%79[^\n]", wagen1.modell);

where the number is one less than the size of the character array (to allow for the \0 character).

Originally Posted by tabstop

Note that fgets keeps the new-line character, which means it is your responsibility to remove it.

%s won't allow for input with spaces in it, so if you wanted that (and it looks like you do!) you would need to use a scanset instead (again with a length given).

Code:

scanf("%79[^\n]", wagen1.modell);

where the number is one less than the size of the character array (to allow for the \0 character).

Thanks for the tip. But it work once only, if twice and more then it comes to an error. Without fflush(stdin) as well. Only errors so or so.

Microsoft write about fflush(): "fflush on input stream is an extension to the C standard"
fflush

Will MS offer a function whose behavior is unclear (for Windows systems)? I will hope no!

The tip twice:


Once only is OK:


The code for that:

Code:

//Daten einlesen - Input data
    printf("\nFirma    : ");
    //scanf("%49[^\n]", wagen1.firma);
    fgets(wagen1.firma, sizeof(wagen1.firma), stdin);
    printf("Modell   : ");
    //fgets(wagen1.modell, sizeof(wagen1.modell), stdin);
    scanf("%49[^\n]", wagen1.modell);
    
    printf("Anzahl PS: ");
    scanf(" %f", &wagen1.ps);
    //do {scanf("%f", &wagen1.ps);} while(getchar() != '\n' && getchar() != EOF);
    printf("Preis    : ");
    scanf(" %f", &wagen1.preis);
    //do {scanf("%f", &wagen1.preis);} while(getchar() != '\n' && getchar() != EOF);
    fflush(stdin);
            
    printf("\nFirma    : ");
    fgets(wagen2.firma, sizeof(wagen2.firma), stdin);
    printf("Modell   : ");
    fgets(wagen2.modell, sizeof(wagen2.modell), stdin);
    
    printf("Anzahl PS: ");
    scanf(" %f", &wagen2.ps);
    //do {scanf("%f", &wagen2.ps);} while(getchar() != '\n' && getchar() != EOF);
    printf("Preis    : ");
    scanf(" %f", &wagen2.preis);
    //do {scanf("%f", &wagen1.preis);} while(getchar() != '\n' && getchar() != EOF);
    fflush(stdin);