Related
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int* create_int_array(){
int* arr;
arr = (int *)calloc(1,sizeof(int));
return arr;
}
char** create_string_array(){
char** arr = calloc(1,sizeof(char));
return arr;
}
void append_int(int* array, int element, int index){
array = (array+index);
*array = element;
}
void append_string(char** array , char* element,int index){
*(array + index) = calloc(1,sizeof(char*));
strcpy(*(array + index),element);
}
void delete_string(char** array, int index){
free(array[index]);
}
void delete_int(int* array,int index){
array[index] = NULL;
}
/////// M A I N F I L E ///////
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "basic_data_file.h"
int main(int argc, char const *argv[])
{
/* code */
char **array;
array = create_string_array();
char *full_name = calloc(strlen("hamza arslan"),sizeof(char*));
strcpy(full_name,"hamza arslan");
char* mail = calloc(strlen("test#gmail.com"),sizeof(char*));
strcpy(mail,"test#gmail.com");
char* address = calloc(strlen("Hacettepe Universty"),sizeof(char*));
strcpy(address,"Hacettepe Universty");
char* statu = calloc(strlen("student"),sizeof(char*));
strcpy(statu,"student");
append_string(array,full_name,0);
append_string(array,mail,1);
append_string(array,address,2);
append_string(array,statu,4);
for(int i=0; i< 3; i++){
printf("%s\n",array[i]);
free(array[i]); // get free double pointer
}
printf("%s\n",array[4]); // because index 3 blow up
free(full_name);
free(mail);
free(address);
free(statu);
return 0;
}
I was try to own my basic array library . As you know else in some languages have high level array types. They are making easy our stocking operation. But in c, it's more complicated especially about string. I have 2 problem in here . First of all , when i give index=3 in append_string function , code blow up with Aborted(core dumped) error.(./run': double free or corruption (out)). Secondly , when i was checking leak memory ,it's get memory leak even i use free. What can i do?
Your create_xy_array functions allocate an array of 1 element, and they stay that way until the very end. When you have a one-element array and index, read/write its second and further elements, C itself happily approves, but the result will not work, it silently destroys everything in its path.
First of all, for having a dynamic array, you have to track its length yourself, C allocations/arrays do not know their own size. So you need a struct, containing the length and a pointer, something like
typedef struct IntArray {
int length;
int *elements;
} IntArray;
Then allocate it, for 0 elements, as there is nothing inside at the beginning:
IntArray* create_int_array() {
IntArray* ret = (IntArray*) malloc(sizeof(IntArray));
ret->length = 0;
ret->elements = NULL;
return ret;
}
void free_int_array(IntArray* arr) {
free(arr->elements);
free(arr);
}
Then you can try putting something inside:
void append_int(IntArray* arr, int element) {
arr->length++;
arr->elements = (int*) realloc(arr->elements, arr->length*sizeof(int));
arr->elements[length-1] = element;
}
(appending means adding something to the end of an array, there is no need for indices here)
And this could go on forever, deletion of an arbitrary element should shift the "upper" part of the array (memcpy) and resize the result to one element smaller or you could track the capacity of the array, which can be larger than its current length (but then it has to be incorporated into the append function and probably others).
(Disclaimer: I hope the snippet is correct, but I do not use C too often - and I can not suggest a good tutorial for the same reason, but that is what you probably need)
Note: I haven't code in C for years and I haven't check the code so double check and let me know.
Based on your description, you are trying to do a Vector.
Therefore, there are different ways that you can handle this.
Approach 1:
Create a structure which will hold the array, the capacity of the array, and the size of the array.
typedef struct StrArray{
int capacity;
int size;
int *integers;
}
The trick here is to take attention when you increase/decrease the capacity.
If you increase the capacity above the size of the array, then:
You need to create a new array with double the capacity
Copy all elements to the new array
Change pointer to new array
Free the memory of the old array
Approach 2
You can extend the previous approach by creating a function which returns a struct which holds the storage plus function pointers to the methods you wish to implement.
typedef struct StrStorage{
int capacity;
int size;
int *integers;
} StrStorage;
typedef struct StrArray {
StrStorage storage;
int (*capacity)(StrArray*);
int (*size)(StrArray*);
StrArray *(*append)(StrArray*, int);
void (*increaseStorage)(StrArray*);
// Add other methods here
} StrArray;
int capacity(StrArray *self) {
return self->storage->capacity;
}
int size(StrArray *self) {
return self->storage->size;
}
StrArray *append(StrArray *self, int integer){
if ((self->capacity() + 1) > self->size()){
self->increaseStorage();
}
// The rest of the magic goes here
return self;
}
StrArray *initializeStrArray(int n) {
StrArray* strArray = malloc(sizeof(StrArray));
strArray->chars = malloc(sizeof(char) * n);
strArray->capacity= capacity;
strArray->append = append;
return strArray;
}
Approach 3:
This approach is a continuation of the previous one.
In order to reduce the memory allocation, you can create an equivalent to a singleton which holds all the manipulation functions and then assi
There will be several crashes, but here is one:
char** arr = calloc(1,sizeof(char));
You are allocating 1 byte which is not sufficient to store a (char *), which needs between 2 and 8 bytes depending on the OS and target machine.
Try this instead:
char** arr = calloc(1,sizeof(char*));
You should double-check each line of code. C is not a forgiving language - mistakes are severely punished.
I have a struct called menu_item that looks like:
struct menu_item
{
char name[ITEM_NAME_LEN+1];
};
And in main I declare an array of pointers to the struct (am I right about this part?):
struct menu_item * menu_items[NUM_MENU_ITEMS];
And also in main I'm trying to call:
init_menu(&menu_items[NUM_MENU_ITEMS]);
init_menu function looks like this:
void menu_init(struct menu_item * menu_items[NUM_MENU_ITEMS])
{
/* allocate memory for each element in the array */
menu_items[NUM_MENU_ITEMS] = (struct menu_item *) malloc(sizeof(struct menu_item));
}
However I'm getting a segmentation error, what am I doing wrong? Thanks in advance.
Take a closer look to your function.
void menu_init(struct menu_item * menu_items[NUM_MENU_ITEMS])
{
/* allocate memory for each element in the array */
menu_items[NUM_MENU_ITEMS] = (struct menu_item *) malloc(sizeof(struct menu_item));
}
You need to carry the size of the array in a second parameter in your function. However, NUM_MENU_ITEMS, seems to be a global #define, thus you don't need to carry a second parameter.
Then you are accessing an out of bound cell, menu_items[NUM_MENU_ITEMS]. I assume you know that the indexing starts from 0 and ends at NUM_MENU_ITEMS-1.
In your function, you need, inside a loop, to allocate memory. Moreover, you don't need to cast what malloc returns.
So, for example, you could do something like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define ITEM_NAME_LEN 15
#define NUM_MENU_ITEMS 3
// Define the struct before main
struct menu_item {
char name[ITEM_NAME_LEN + 1];
};
// Give a synonym. Now struct menu_item is the same with menu_item_t.
// Notice the _t extension, which implies that this is a typedef.
typedef struct menu_item menu_item_t;
/**
* Given a pointer 'p' to an array of pointers
* (of type menu_item_t), allocate memory for
* every cell of the array.
*/
void init_menu(menu_item_t* p[]) {
int i;
for(i = 0; i < NUM_MENU_ITEMS; ++i) {
// for every cell of our array, allocate memory
p[i] = malloc(sizeof(menu_item_t));
// check that allocation for the i-th cell is OK
if(!p[i]) {
printf("Error in allocating %d item!\n\n", i);
return;
}
}
}
/**
* Given a pointer 'p' to an array of pointers
* (of type menu_item_t), de-allocate memory for
* every cell of the array.
*/
void delete_menu(menu_item_t* p[]) {
int i;
for(i = 0; i < NUM_MENU_ITEMS; ++i) {
// free the memory we had allocated for the i-th cell
free(p[i]);
// set the pointer to NULL
p[i] = NULL;
}
}
void fill(menu_item_t* p[]) {
int i;
for(i = 0; i < NUM_MENU_ITEMS; ++i) {
strcpy(p[i]->name, "myitem");
}
}
void print(menu_item_t* p[]) {
int i;
for(i = 0; i < NUM_MENU_ITEMS; ++i) {
printf("%s\n", p[i]->name);
}
}
int main(void) {
// Declare an array of pointers of menu_items_t.
// The size of the array is NUM_MENU_ITEMS
menu_item_t *menu_items[NUM_MENU_ITEMS];
init_menu(menu_items);
fill(menu_items);
print(menu_items);
delete_menu(menu_items);
return 0;
}
When I deal with structs, I always have this example on mind.
You are calling your function as
init_menu(&menu_items[NUM_MENU_ITEMS]);
This does not make sense. Expression &menu_items[NUM_MENU_ITEMS] creates a pointer to element with index NUM_MENU_ITEMS. Such element does not exist. Your array has elements numbered from 0 to NUM_MENU_ITEMS - 1. There's no element with index NUM_MENU_ITEMS.
Expression &menu_items[NUM_MENU_ITEMS] produces a pointer into the uncharted memory past the end of the array. You pass that pointer to the function. Later you are trying to use that pointer as if it were your array. You write into that uncharted memory, which causes a crash.
If you want to pass your array to the function, just pass it. Your function should be called as
init_menu(menu_items);
That's it. There's no need to create any pointers to any elements with strange indices.
Later, inside your function you are again trying to access element NUM_MENU_ITEMS of your array
menu_items[NUM_MENU_ITEMS] = ...
This does not make sense either for the very same reasons.
I have a program which creates an array or struct and go through it for processing. Initially it initialize the array with the defined nyumber of elements. Then for some number of element in array, the name is assigned.
I pretend the code that is equal to my scenario which is tested in codebloc and get the similar error. The problem is described in comments.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct _car {
char *name;
int year;
} Car;
char *getCarName(char *name, int var);
void processCar();
void printCars(Car car[]);
int INCREMENT = 10;
int main(void)
{
processCar();
return 0;
}
void processCar()
{
// create car array with amount of INCREMENT
Car CAR_ARRAY[INCREMENT];
int a=0;
// This function assign name for Car amount 10 less than INCREMENT
while (a<INCREMENT - 2) {
char *carName;
carName = getCarName(&carName, a);
CAR_ARRAY[a].name = malloc(strlen(carName) + 1);
strcpy(CAR_ARRAY[a].name, carName);
a++;
}
printCars(CAR_ARRAY);
}
void printCars(Car car[])
{
printf("IN Car \n");
int a = 0;
// when try to call name for car amount equals to INCREMENT program terminates.
while(a<INCREMENT) {
if (car[a].name != NULL) // checking if NULL
printf("Car Name : %d -> %s\n", a, car[a].name);
a++;
}
}
char *getCarName(char *name, int var)
{
name = "Toyota";
return name;
}
What is the right way to check the struct value on struct array whether it can be called?
EDIT
I created a hack to do this as follows.
// added these right after creating array
for (a = 0; a < INCREMENT; a++)
CAR_ARRAY[a].name = NULL;
I dont know if it is a standard way or not. pls advice.
You are checking for NULL before printing, which is a good idea, but it doesn't help you here, because your last two cars are uninitialised and likely contain garbage: The name pointer is not NULL, but doesn't point to a valid address either. Segmentation violation ensues.
You should initialise all cars, not only INCREMENT - 2. Alternatively, you could initialise your cars to zero by calling memset before your initialisation:
memset(CAR_ARRAY, 0, sizeof(Car) * INCREMENT);
As an aside, the way you deal with getCarName is rather shaky as well. At the moment, your name is a pointer to a string literal. Your local variable carName does a half-hearted double duty: You try to pass it by reference (but essentially you don't) and you also return it.
Basically, you could do this in one of two ways. The easier one here is to return a pointer. in that case, you don't have to pass any string:
char *getCarName(int var)
{
static char *names[3] = {"Toyota", "Dodge", "Peugeot"};
return names[var % 3];
}
and call it like so:
char *carName = getCarName(&carName, a);
Alternatively, you could pass a char pointer by reference, i.e. as pointer to pointer to char. In that case, you don't have to return anything:
void getCarName(char **name, int var)
{
static char* names[3] = {"Toyota", "Dodge", "Peugeot"};
*name = names[var % 3];
}
Call it like so:
char *carName;
getCarName(&carName, a);
There are other scenarios here, for example if you just pass a char pointer and have getCarName fill it, but I'll leave that for now - it would make everything even more complicated.
I know how to create an array of structs but with a predefined size. However is there a way to create a dynamic array of structs such that the array could get bigger?
For example:
typedef struct
{
char *str;
} words;
main()
{
words x[100]; // I do not want to use this, I want to dynamic increase the size of the array as data comes in.
}
Is this possible?
I've researched this: words* array = (words*)malloc(sizeof(words) * 100);
I want to get rid of the 100 and store the data as it comes in. Thus if 76 fields of data comes in, I want to store 76 and not 100. I'm assuming that I don't know how much data is coming into my program. In the struct I defined above I could create the first "index" as:
words* array = (words*)malloc(sizeof(words));
However I want to dynamically add elements to the array after. I hope I described the problem area clearly enough. The major challenge is to dynamically add a second field, at least that is the challenge for the moment.
I've made a little progress however:
typedef struct {
char *str;
} words;
// Allocate first string.
words x = (words) malloc(sizeof(words));
x[0].str = "john";
// Allocate second string.
x=(words*) realloc(x, sizeof(words));
x[1].FirstName = "bob";
// printf second string.
printf("%s", x[1].str); --> This is working, it's printing out bob.
free(x); // Free up memory.
printf("%s", x[1].str); --> Not working since its still printing out BOB even though I freed up memory. What is wrong?
I did some error checking and this is what I found. If after I free up memory for x I add the following:
x=NULL;
then if I try to print x I get an error which is what I want. So is it that the free function is not working, at least on my compiler? I'm using DevC??
Thanks, I understand now due to:
FirstName is a pointer to an array of char which is not being allocated by the malloc, only the pointer is being allocated and after you call free, it doesn't erase the memory, it just marks it as available on the heap to be over written later. – MattSmith
Update
I'm trying to modularize and put the creation of my array of structs in a function but nothing seems to work. I'm trying something very simple and I don't know what else to do. It's along the same lines as before, just another function, loaddata that is loading the data and outside the method I need to do some printing. How can I make it work? My code is as follows:
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# include <ctype.h>
typedef struct
{
char *str1;
char *str2;
} words;
void LoadData(words *, int *);
main()
{
words *x;
int num;
LoadData(&x, &num);
printf("%s %s", x[0].str1, x[0].str2);
printf("%s %s", x[1].str1, x[1].str2);
getch();
}//
void LoadData(words *x, int * num)
{
x = (words*) malloc(sizeof(words));
x[0].str1 = "johnnie\0";
x[0].str2 = "krapson\0";
x = (words*) realloc(x, sizeof(words)*2);
x[1].str1 = "bob\0";
x[1].str2 = "marley\0";
*num=*num+1;
}//
This simple test code is crashing and I have no idea why. Where is the bug?
You've tagged this as C++ as well as C.
If you're using C++ things are a lot easier. The standard template library has a template called vector which allows you to dynamically build up a list of objects.
#include <stdio.h>
#include <vector>
typedef std::vector<char*> words;
int main(int argc, char** argv) {
words myWords;
myWords.push_back("Hello");
myWords.push_back("World");
words::iterator iter;
for (iter = myWords.begin(); iter != myWords.end(); ++iter) {
printf("%s ", *iter);
}
return 0;
}
If you're using C things are a lot harder, yes malloc, realloc and free are the tools to help you. You might want to consider using a linked list data structure instead. These are generally easier to grow but don't facilitate random access as easily.
#include <stdio.h>
#include <stdlib.h>
typedef struct s_words {
char* str;
struct s_words* next;
} words;
words* create_words(char* word) {
words* newWords = malloc(sizeof(words));
if (NULL != newWords){
newWords->str = word;
newWords->next = NULL;
}
return newWords;
}
void delete_words(words* oldWords) {
if (NULL != oldWords->next) {
delete_words(oldWords->next);
}
free(oldWords);
}
words* add_word(words* wordList, char* word) {
words* newWords = create_words(word);
if (NULL != newWords) {
newWords->next = wordList;
}
return newWords;
}
int main(int argc, char** argv) {
words* myWords = create_words("Hello");
myWords = add_word(myWords, "World");
words* iter;
for (iter = myWords; NULL != iter; iter = iter->next) {
printf("%s ", iter->str);
}
delete_words(myWords);
return 0;
}
Yikes, sorry for the worlds longest answer. So WRT to the "don't want to use a linked list comment":
#include <stdio.h>
#include <stdlib.h>
typedef struct {
char** words;
size_t nWords;
size_t size;
size_t block_size;
} word_list;
word_list* create_word_list(size_t block_size) {
word_list* pWordList = malloc(sizeof(word_list));
if (NULL != pWordList) {
pWordList->nWords = 0;
pWordList->size = block_size;
pWordList->block_size = block_size;
pWordList->words = malloc(sizeof(char*)*block_size);
if (NULL == pWordList->words) {
free(pWordList);
return NULL;
}
}
return pWordList;
}
void delete_word_list(word_list* pWordList) {
free(pWordList->words);
free(pWordList);
}
int add_word_to_word_list(word_list* pWordList, char* word) {
size_t nWords = pWordList->nWords;
if (nWords >= pWordList->size) {
size_t newSize = pWordList->size + pWordList->block_size;
void* newWords = realloc(pWordList->words, sizeof(char*)*newSize);
if (NULL == newWords) {
return 0;
} else {
pWordList->size = newSize;
pWordList->words = (char**)newWords;
}
}
pWordList->words[nWords] = word;
++pWordList->nWords;
return 1;
}
char** word_list_start(word_list* pWordList) {
return pWordList->words;
}
char** word_list_end(word_list* pWordList) {
return &pWordList->words[pWordList->nWords];
}
int main(int argc, char** argv) {
word_list* myWords = create_word_list(2);
add_word_to_word_list(myWords, "Hello");
add_word_to_word_list(myWords, "World");
add_word_to_word_list(myWords, "Goodbye");
char** iter;
for (iter = word_list_start(myWords); iter != word_list_end(myWords); ++iter) {
printf("%s ", *iter);
}
delete_word_list(myWords);
return 0;
}
If you want to dynamically allocate arrays, you can use malloc from stdlib.h.
If you want to allocate an array of 100 elements using your words struct, try the following:
words* array = (words*)malloc(sizeof(words) * 100);
The size of the memory that you want to allocate is passed into malloc and then it will return a pointer of type void (void*). In most cases you'll probably want to cast it to the pointer type you desire, which in this case is words*.
The sizeof keyword is used here to find out the size of the words struct, then that size is multiplied by the number of elements you want to allocate.
Once you are done, be sure to use free() to free up the heap memory you used in order to prevent memory leaks:
free(array);
If you want to change the size of the allocated array, you can try to use realloc as others have mentioned, but keep in mind that if you do many reallocs you may end up fragmenting the memory. If you want to dynamically resize the array in order to keep a low memory footprint for your program, it may be better to not do too many reallocs.
This looks like an academic exercise which unfortunately makes it harder since you can't use C++. Basically you have to manage some of the overhead for the allocation and keep track how much memory has been allocated if you need to resize it later. This is where the C++ standard library shines.
For your example, the following code allocates the memory and later resizes it:
// initial size
int count = 100;
words *testWords = (words*) malloc(count * sizeof(words));
// resize the array
count = 76;
testWords = (words*) realloc(testWords, count* sizeof(words));
Keep in mind, in your example you are just allocating a pointer to a char and you still need to allocate the string itself and more importantly to free it at the end. So this code allocates 100 pointers to char and then resizes it to 76, but does not allocate the strings themselves.
I have a suspicion that you actually want to allocate the number of characters in a string which is very similar to the above, but change word to char.
EDIT: Also keep in mind it makes a lot of sense to create functions to perform common tasks and enforce consistency so you don't copy code everywhere. For example, you might have a) allocate the struct, b) assign values to the struct, and c) free the struct. So you might have:
// Allocate a words struct
words* CreateWords(int size);
// Assign a value
void AssignWord(word* dest, char* str);
// Clear a words structs (and possibly internal storage)
void FreeWords(words* w);
EDIT: As far as resizing the structs, it is identical to resizing the char array. However the difference is if you make the struct array bigger, you should probably initialize the new array items to NULL. Likewise, if you make the struct array smaller, you need to cleanup before removing the items -- that is free items that have been allocated (and only the allocated items) before you resize the struct array. This is the primary reason I suggested creating helper functions to help manage this.
// Resize words (must know original and new size if shrinking
// if you need to free internal storage first)
void ResizeWords(words* w, size_t oldsize, size_t newsize);
In C++, use a vector. It's like an array but you can easily add and remove elements and it will take care of allocating and deallocating memory for you.
I know the title of the question says C, but you tagged your question with C and C++...
Another option for you is a linked list. You'll need to analyze how your program will use the data structure, if you don't need random access it could be faster than reallocating.
Your code in the last update should not compile, much less run. You're passing &x to LoadData. &x has the type of **words, but LoadData expects words* . Of course it crashes when you call realloc on a pointer that's pointing into stack.
The way to fix it is to change LoadData to accept words** . Thi sway, you can actually modify the pointer in main(). For example, realloc call would look like
*x = (words*) realloc(*x, sizeof(words)*2);
It's the same principlae as in "num" being int* rather than int.
Besides this, you need to really figure out how the strings in words ere stored. Assigning a const string to char * (as in str2 = "marley\0") is permitted, but it's rarely the right solution, even in C.
Another point: non need to have "marley\0" unless you really need two 0s at the end of string. Compiler adds 0 tho the end of every string literal.
For the test code: if you want to modify a pointer in a function, you should pass a "pointer to pointer" to the function. Corrected code is as follows:
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
typedef struct
{
char *str1;
char *str2;
} words;
void LoadData(words**, int*);
main()
{
words **x;
int num;
LoadData(x, &num);
printf("%s %s\n", (*x[0]).str1, (*x[0]).str2);
printf("%s %s\n", (*x[1]).str1, (*x[1]).str2);
}
void LoadData(words **x, int *num)
{
*x = (words*) malloc(sizeof(words));
(*x[0]).str1 = "johnnie\0";
(*x[0]).str2 = "krapson\0";
*x = (words*) realloc(*x, sizeof(words) * 2);
(*x[1]).str1 = "bob\0";
(*x[1]).str2 = "marley\0";
*num = *num + 1;
}
Every coder need to simplify their code to make it easily understood....even for beginners.
So array of structures using dynamically is easy, if you understand the concepts.
// Dynamically sized array of structures
#include <stdio.h>
#include <stdlib.h>
struct book
{
char name[20];
int p;
}; //Declaring book structure
int main ()
{
int n, i;
struct book *b; // Initializing pointer to a structure
scanf ("%d\n", &n);
b = (struct book *) calloc (n, sizeof (struct book)); //Creating memory for array of structures dynamically
for (i = 0; i < n; i++)
{
scanf ("%s %d\n", (b + i)->name, &(b + i)->p); //Getting values for array of structures (no error check)
}
for (i = 0; i < n; i++)
{
printf ("%s %d\t", (b + i)->name, (b + i)->p); //Printing values in array of structures
}
scanf ("%d\n", &n); //Get array size to re-allocate
b = (struct book *) realloc (b, n * sizeof (struct book)); //change the size of an array using realloc function
printf ("\n");
for (i = 0; i < n; i++)
{
printf ("%s %d\t", (b + i)->name, (b + i)->p); //Printing values in array of structures
}
return 0;
}
If you want to grow the array dynamically, you should use malloc() to dynamically allocate some fixed amount of memory, and then use realloc() whenever you run out. A common technique is to use an exponential growth function such that you allocate some small fixed amount and then make the array grow by duplicating the allocated amount.
Some example code would be:
size = 64; i = 0;
x = malloc(sizeof(words)*size); /* enough space for 64 words */
while (read_words()) {
if (++i > size) {
size *= 2;
x = realloc(sizeof(words) * size);
}
}
/* done with x */
free(x);
Here is how I would do it in C++
size_t size = 500;
char* dynamicAllocatedString = new char[ size ];
Use same principal for any struct or c++ class.
I'm trying to split a string every X amount of characters, and then store each line in an array of structs. However, I'm wondering what would be a short and efficient way of doing it. I thought that maybe I could use sscanf, but not very sure how to. Any help will be appreciated. So far I have:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct st {char *str;};
int main ()
{
struct st **mystruct;
char tmp[] = "For configuration options (arch/xxx/config.in, and all the Config.in files),somewhat different indentation is used.";
size_t max = 20, j = 0; // max length of string
size_t alloc = strlen(tmp)/max + 1;
mystruct = malloc(alloc * sizeof *mystruct);
for (j = 0; j < alloc; j++)
mystruct[j] = malloc(sizeof *mystruct[j]);
const char *ptr = tmp;
char field [ max ];
int n;
while (*ptr != '\0') {
int line = sscanf(ptr, "%s", field, &n); // not sure how to use max in here
mystruct[j]->str = field;
field[0]='\0';
if (line == 1)
ptr += n;
if ( n != max )
break;
++ptr;
++j;
}
return 0;
}
So when I iterate over my struct, I can get something like:
For configuration op
tions (arch/xxx/conf
ig.in, and all the C
onfig.in files),some
what different inden
tation is used.
You could use strncpy.
FYI:
char field [ max ];
while (...) {
mystruct[j]->str = field;
Two problems with this: (1) every struct in your array is going to end up pointing at the same string, which will have the value of the last thing you scanned, (2) they are pointing to a variable on the stack, so when this function returns they will be trashed. That doesn't manifest itself visibly here (e.g. your program doesn't explode) because the function happens to be 'main', but if you moved this to a separate routine and called it to parse a string, you'd get back garbage.
mystruct doesn't need to be pointer to pointer. For a 1D array, just allocate a block N * sizeof *myarray for N elements.
A common C idiom when dealing with structs is to use typedef so you don't have to type struct foo all the time. For instance:
typedef struct {
int x, y;
} point;
Now instead of typing struct point pt you can just say point pt.
If your string is not going to change after you split it up, I'd recommend using a struct like this:
struct st {
char *begin;
char *end;
};
or the alternative:
struct st {
char *s;
size_t len;
};
Then instead of creating all those new strings, just mark where each one begins and ends in your struct. Keep the original string in memory.
One option is to do it character-by-character.
Calculate the number of lines as you are currently doing.
Allocate memory = (strlen(tmp) + number_of_lines) * sizeof(char)
Walk through your input string, copying characters from the input to the newly allocated memory. Every 20th character, insert a null byte to delimit that string. Save a pointer to the beginning of each line in your array of structs.
Its easy enough?
#define SMAX 20
typedef struct {char str[SMAX+1];} ST;
int main()
{
ST st[SMAX]={0};
char *tmp = "For configuration options (arch/xxx/config.in, and all the Config.in files),somewhat different indentation is used.";
int i=0,j;
for( ; (st[i++]=*(ST*)tmp).str[SMAX]=0 , strlen(tmp)>=SMAX; tmp+=SMAX );
for( j=0;j<i;++j )
puts(st[j].str);
return 0;
}
You may use (non C standard but GNU) function strndup().
#define _GNU_SOURCE
#include <string.h>
struct st {char *str;};
int main ()
{
struct st *mystruct; /* i wonder if there's need for double indirection... */
char tmp[] = "For configuration options (arch/xxx/config.in, and all the Config.in files),somewhat different indentation is used.";
size_t max = 20, j = 0; // max length of string
size_t alloc = (strlen(tmp) + max - 1)/max; /* correct round up */
mystruct = malloc(alloc * sizeof mystruct);
if(!mystruct) return 1; /* never forget testing if allocation failed! */
for(j = 0; j<alloc; j++)
{
mystruct[j].str = strndup(tmp+alloc*max, max);
}
}