The module that swaps row to make an array sorted in ascii ascending order keeps returning error.
const int MAX = 10;
const int MAX_STR = 80;
void asciiOrder(char (*buffer)[MAX_STR]);
void asciiOrder(char (*buffer)[MAX_STR]) {
char * temp;
for (int i = 0; i < sizeof(buffer) / sizeof (buffer[0]) - 1; i++) {
for (int j = 1; i + j < sizeof(buffer) / sizeof(buffer[0]); j++) {
for (int k = 0; k < strlen(buffer[i]) && buffer[i][k] != NULL; k++) {
if (buffer[i][k] > buffer[i+j][k]) {
temp = buffer[i+j];
buffer[i+j] = buffer[i];
buffer[i] = temp;
break;
}
}
}
}
}
And this is the error I got from the entire code:
practice102.c:87:23: error: assignment to expression with array type
buffer[i+j] = buffer[i];
^
practice102.c:88:21: error: assignment to expression with array type
buffer[i] = temp;
I searched other posts but still don't know why.
How to solve this problem?
C forbidden to assign a 2D array without specify the two index.
You have to write something like
buffer[a][b] = buffer[c][d]
whatever your a,b,c,d are.
Also be sure that your buffer temp are filled and/or allocated.
Related
I'm trying to assign the elements of string str[] to rev[] using this code below, but it keeps giving me the error:
"string subscript out of range" error.
How do I correct this?
for (int i = 0; i <= str.length(); i++)
{
for (int j = str.length(); j >= 0; j--)
{
rev[i] = str[j];
}
}
For an array index range from 0 to array size - 1.
You don't need two loops to reverse an array.
In java you can do reversal like this:
int length = str.length - 1;
for (int i = 0; i <= str.length-1; i++) {
rev[length - i] = str[i];
}
I am a bit of a beginner in C language. I was trying out a task of dynamically reallocating memory as the input comes through(although for this test I am doing a normal task, later will try to scale it up). the issue I am facing is I am unable to access the memory while writing into it. Can anyone please help me understand where I am going wrong in this code. thanks in advance.
code:
#include<stdio.h>
#include<stdlib.h>
struct ai {
int* a;
char* b;
};
int main()
{
struct ai *test;
test = (struct ai*) malloc(sizeof(struct ai));
test[0].a = (int*)malloc(sizeof(int));
test[0].b = (char*)malloc(sizeof(char));
/// storing info
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 4; j++)
{
test[i].a[j] = j;
test[i].b[j] = 65 + j;
test[i].a = (int *) realloc(test[i].a, (j + 2) * sizeof(int));
test[i].b = (char*) realloc(test[i].b, (j + 2) * sizeof(char));
}
test = (struct ai*)realloc(test, (i + 2) * sizeof(struct ai));
}
// printing the block out
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 4; j++)
{
printf("%d , %c\n", test[i].a[j], test[i].b[j]);
}
}
return 0;
} ```
You have missing initialization of your pointers and some other issues...
int main()
{
struct ai *test;
test = (struct ai*) malloc(sizeof(struct ai));
test[0].a = (int*)malloc(sizeof(int));
test[0].b = (char*)malloc(sizeof(char));
In C you should not cast the result of malloc. In best case it is useless. In worst case it hides real problems.
/// storing info
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 4; j++)
{
test[i].a[j] = j;
test[i].b[j] = 65 + j;
Here comes the reason for your segmentation fault:
You do not have any memory reserved for a and b except for the first element test[0]. All other array elements test[i] do not contain any useful data. Dereferencing these pointers is undefined behaviour.
You must allocate memory for each field after you enlarged your array.
test[i].a = (int *) realloc(test[i].a, (j + 2) * sizeof(int));
test[i].b = (char*) realloc(test[i].b, (j + 2) * sizeof(char));
You should never assign the return value of realloc to the same variable that you passed into the function. In case of an error you will get NULL return value and then your initiali pointer is lost.
Also here: don't cast for realloc as well.
}
test = (struct ai*)realloc(test, (i + 2) * sizeof(struct ai));
Same here: Don't assign to same variable and don't cast the result of realloc.
Finally: Here goes the missing part:
test[i+1].a = malloc(sizeof(*test[0].a));
test[i+1].b = malloc(sizeof(*test[0].b));
}
Of course you should check all return values for error results.
Not related to the segmentation fault, but still worth to fix:
You increment the size of each array after you used the last element.
This prepares the new element for being filled in next iteration of the loops. But in case of the last iteration it allocated an unused element for both the intern pointers a and b as well as the outer array test.
You will have some unused elements:
test[0].a[4]
test[0].b[4]
test[1].a[4]
test[1].b[4]
test[2].a[0]
test[2].b[0]
An improved solution could look like this (not tested)
I start with each pointer being NULL and use realloc right before the new element is used to avoid the extra elements.
int main(void)
{
struct ai *test = NULL
void *tmp;
// storing info
for (int i = 0; i < 2; i++)
{
tmp = realloc(test, (i+1) * sizeof(*test))
if (tmp == NULL)
exit(1);
test = tmp;
test[i].a = NULL;
test[i].b = NULL;
for (int j = 0; j < 4; j++)
{
tmp = realloc(test[i].a, (j+1) * sizeof(test[i].a[0]));
if (tmp == NULL)
exit(1);
test[i].a = tmp;
tmp = realloc(test[i].b, (j+1) * sizeof(test[i].b[0]));
if (tmp == NULL)
exit(1);
test[i].b = tmp;
test[i].a[j] = j;
test[i].b[j] = 65 + j;
}
}
// printing the block out
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 4; j++)
{
printf("%d , %c\n", test[i].a[j], test[i].b[j]);
}
}
return 0;
}
Basically, my question is how can I use some part of an array? For example, first byte equal to structure.code then other four byte equal structure.timestamps etc. I'm new, thanks for understands.
My function:
void GlimpseStructures(char buffer[])
{
int i = 0;
HeartbeatPackage a;
a.to_little_endian();
a.code = buffer[0];
for (i = 1; i < 5; i++)
{
a.timestamp += buffer[i];
}
for (i = 5; i < 9; i++)
{
buffer[i] += a.nanosecond_elapsed;
printf("nanosecond:%d/n", a.nanosecond_elapsed);
}
}
I have to make a program that sort strings (with exact length 7 chars) by using radix sort. I already made a function that sort each column separately. My problem is how to make the whole string move, not just one char. It's really problematic for me to see how should it work in C.
I made one array "char strings[3][8]" and "char output[3][8]" to get sorted 3 strings with exact 7 chars in each one. For example sorting these strings:
strcpy(strings[0], "kupbars");
strcpy(strings[1], "daparba");
strcpy(strings[2], "jykaxaw");
In output I get:
dakaaaa
juparbs
kypbxrw
Each column is sorted correctly but chars don't stick together. I tried many ways for 3 hours but nothing works.
My code looks like this:
void countingSort(char a[][8], char b[][8]) {
int c[123];
for (int pos = 6; pos >= 0; pos--) {
for (int i = 0; i < 123; i++)
c[i] = 0;
for (int i = 0; i < 3; i++)
c[(int)a[i][pos]]++;
for (int i = 1; i < 123; i++)
c[i] += c[i - 1];
for (int i = 2; i >= 0; i--) {
b[--c[(int)a[i][pos]]][pos] = a[i][pos];
}
}
}
(There are constants limiting string length etc. because it's easy to change it to variable - I just focused on getting this program work properly.)
Try changing the loop to move an entire string:
for (int i = 2; i >= 0; i--) {
int k = --c[(int)a[i][pos]];
for(int j = 0; j < 8; j++) {
b[k][j] = a[i][j];
}
}
You could do a circular list but it's a little overhead. I propose you to use memmove().
#include <string.h>
void array_move_forward(char array[3][8]) {
for (int i = 0; i < 3; i++) {
char tmp = array[i][6];
memmove(array[i] + 1, array[i], 6);
array[i][0] = tmp;
}
}
void array_move_rewind(char array[3][8]) {
for (int i = 0; i < 3; i++) {
char tmp = array[i][0];
memmove(array[i], array[i] + 1, 6);
array[i][6] = tmp;
}
}
A other solution would be to manipulate your string yourself and using a index, that indicate the first letter of your string.
{
char str[7];
int i = 0;
...
int j = i;
for (int k = 0; k < 7; k++) {
char tmp = str[j++ % 7];
}
}
With that you could rotate your string just with i++ or i--.
struct my_string_radix {
char str[7];
int begin;
}
I got this error in my rc4 algorithm, it works well, but i got this error every time when the message is too big, like 1000kB, here is the code:
char* rc4(const int* key, int key_size, char* buff, int buff_size){
int i, j, k;
int s[255], rk[255]; //rk = random_key
char* encrypted = alloc_char_buffer(buff_size);
for (i = 0; i < 255; i++){
s[i] = i;
rk[i] = key[i%key_size];
}
j = 0;
for (i = 0; i < 255; i++){
j = (j + s[j] + rk[i]) % 256;
SWITCH(s + i, s + j);
}
i = 0;
j = 0;
for (k = 0; k < buff_size; k++){
i = (i + 1) % 256;
j = (j + s[i]) % 256;
SWITCH(s + i, s + j);
//try{
//}
//catch ()
encrypted[k] = (char)(s[(s[i] + s[j]) % 256] ^ (int)buff[k]);
}
encrypted[buff_size] = 0;
return encrypted;
}
at the end o the last loop i got this error, i think this is some type of buffer overflow error, the only variable able to do that is the 'encrypted' but at the end of the loop, the value of the variable 'k' have the exactly same value of 'buff_size' that is used to alloc memory for 'encrypted', if someone can help i'll thank you
the 'encrypted' is "non-null terminated", so if the string have 10 bytes i will allocate only 10 bytes, not 11 for the '\0'
if you need, here is the code for alloc_char_buffer(unsigned int)
char* alloc_char_buffer(unsigned int size){
char* buff = NULL;
buff = (char*)calloc(size+1, sizeof(char));
if (!buff)
_error("program fail to alloc memory.");
return buff;
}
SWITCH:
//inversão de valores
void SWITCH(int *a, int *b){
*(a) = *(a) ^ *(b); //a random number
*(b) = *(a) ^ *(b); //get a
*(a) = *(a) ^ *(b); //get b
}
char* encrypted = alloc_char_buffer(buff_size);
/* ... */
encrypted[buff_size] = 10;
Here is the problem. You allocate buff_size elements. Thus, the last valid index is buff_size-1, not buff_size.
Another issue:
j = (j + s[j] + rk[i]) % 256;
Thus the range of j is [0, 255], but the legal index of s is only [0, 254]. You should either declare s as a 256-element array or review the algorithm implementation.
Your following line is creating the problem as you are trying to access beyond your allocated memory.
encrypted[buff_size] = 10;
Additionally, you should avoid use calloc instead of writing your own function alloc_char_buffer. It would allocate memory and initialize with 0.
calloc(buff_size, sizeof(char));