C Language, making pointers to structure elements using array elements

making pointers to structure elements using array elements

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rock_ramm #1 / 3	making pointers to structure elements using array elements I wanted to know, and I'm sure there is a way, to build pointer names using the contents of an array available to a function. I guess my real question is this: How to I get a character representation from a pointer, such as pointer="name"; appended to another pointer name like current_contact->(the appended name here) I'd love to make a function that takes a structure pointer and an array pointer and updates all the elements of a linked list using just the pointer of an array to specify the elements. the following is some of the code. struct contacts { / keeps basic contact info and is a linked list / char name[50]; char email[50]; char phone[50]; struct contacts next; Quote: }; char elements[3][6]={{"Name"},{"Email"},{"Phone"}}; /* used to format calls for the purposes of learning this concept / { ... Quote: } void add_contact(struct contacts current_contact) { int counter; for (counter=0;counter <3;counter++) { /* counter used for now since I'm lazy and don't want to write array length stuff yet / printf("\n%s of contact: ",(elements+counter)); /* this works as intended / note* current_contact->(how ever I manage to convert the contents that elements+counter points to to describe the pointer) scanf("%s",current_contact->elements+counter); /* I REALLY wish the documentation I found for fgets and fscanf wasn't so freaking obfuscated manybe someone should try writing it in english sometime. */ }
Sun, 05 Sep 2004 12:49:17 GMT

Joona I Palast #2 / 3	making pointers to structure elements using array elements Quote: > I wanted to know, and I'm sure there is a way, to build pointer names > using the contents of an array available to a function. I guess my > real question is this: > How to I get a character representation from a pointer, such as > pointer="name"; appended to another pointer name like > current_contact->(the appended name here) > I'd love to make a function that takes a structure pointer and an > array pointer and updates all the elements of a linked list using just > the pointer of an array to specify the elements. > the following is some of the code. > struct contacts { / keeps basic contact info and is a > linked list / > char name[50]; > char email[50]; > char phone[50]; > struct contacts next; > }; > char elements[3][6]={{"Name"},{"Email"},{"Phone"}}; /* used to > format calls for the purposes of learning this concept / What you ask for cannot be done in C. In C, the names of the structure fields only exist during before compilation, in the produced executable they are replaced by raw addresses. You will have to simulate it by having a look-up table from strings to addresses, something like this: struct contacts { char name[50]; char email[50]; char phone[50]; struct contacts next; Quote: }; char elements[3][6]={"Name", "Email", "Phone"}; int offsets[3]; struct contacts mycontacts; offsets[0]=&mycontacts.name - &mycontacts; offsets[1]=&mycontacts.email - &mycontacts; offsets[2]=&mycontacts.phone - &mycontacts; Then when you get the name of a field in a string you will have to look each of these fields up like this: struct contacts newcontacts; char s[20]; int i; void *p=NULL; printf("Enter field name: "); fflush(stdout); fgets(s, 20, stdin); for (i=0; i<3; i++) if (!strcmp(elements[i], s)) p=&newcontacts + offsets[i]; if (p!=NULL) { printf("Enter field value: "); fflush(stdout); fgets(p, 50, stdin); Quote: } -- \| Kingpriest of "The Flying Lemon Tree" G++ FR FW+ M- #108 D+ ADA N+++\| \| http://www.helsinki.fi/~palaste W++ B OP+ \| \----------------------------------------- Finland rules! ------------/ "You have moved your mouse, for these changes to take effect you must shut down and restart your computer. Do you want to restart your computer now?" - Karri Kalpio
Sun, 05 Sep 2004 12:57:57 GMT

rob #3 / 3	making pointers to structure elements using array elements Quote: > > I wanted to know, and I'm sure there is a way, to build pointer names > > using the contents of an array available to a function. I guess my > > real question is this: > > How to I get a character representation from a pointer, such as > > pointer="name"; appended to another pointer name like > > current_contact->(the appended name here) > > I'd love to make a function that takes a structure pointer and an > > array pointer and updates all the elements of a linked list using just > > the pointer of an array to specify the elements. > > the following is some of the code. > > struct contacts { / keeps basic contact info and is a > > linked list / > > char name[50]; > > char email[50]; > > char phone[50]; > > struct contacts next; > > }; > > char elements[3][6]={{"Name"},{"Email"},{"Phone"}}; /* used to > > format calls for the purposes of learning this concept / > What you ask for cannot be done in C. In C, the names of the structure > fields only exist during before compilation, in the produced executable > they are replaced by raw addresses. > You will have to simulate it by having a look-up table from strings to > addresses, something like this: > struct contacts { > char name[50]; > char email[50]; > char phone[50]; > struct contacts next; > }; > char elements[3][6]={"Name", "Email", "Phone"}; > int offsets[3]; > struct contacts mycontacts; > offsets[0]=&mycontacts.name - &mycontacts; > offsets[1]=&mycontacts.email - &mycontacts; > offsets[2]=&mycontacts.phone - &mycontacts; do you hate offsetof()? I'm fairly sure that's what they put it in stddef.h for. - Hide quoted text - - Show quoted text - Quote: > Then when you get the name of a field in a string you will have to > look each of these fields up like this: > struct contacts newcontacts; > char s[20]; > int i; > void *p=NULL; > printf("Enter field name: "); > fflush(stdout); > fgets(s, 20, stdin); > for (i=0; i<3; i++) > if (!strcmp(elements[i], s)) > p=&newcontacts + offsets[i]; > if (p!=NULL) { > printf("Enter field value: "); > fflush(stdout); > fgets(p, 50, stdin); > } > -- > \| Kingpriest of "The Flying Lemon Tree" G++ FR FW+ M- #108 D+ ADA N+++\| > \| http://www.helsinki.fi/~palaste W++ B OP+ \| > \----------------------------------------- Finland rules! ------------/ > "You have moved your mouse, for these changes to take effect you must shut down > and restart your computer. Do you want to restart your computer now?" > - Karri Kalpio
Mon, 06 Sep 2004 02:24:41 GMT

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