As marked in the code, the first printf() rightfully prints only the i-th line of the matrix. But outiside the loop, both printf() and strcat() act on the whole matrix from i-th line on as a single-lined string. This means that
printf("%s\n",m_cfr[0])
will print whole matrix, but m_cfr[i] will print whole matrix from the i-th line on. char* string is a single lined string with no spaces.
trasp(char* string)
{
int row = strlen(string) / 5;
char m[row][5];
char m_cfr[row][5];
char cfr[row*5];
memset(cfr, 0, row * 5);
int key[5] = {3, 1, 2, 0, 4};
int k = 0;
for (i = 0 ; i < row ; i++)
{
strncpy(m[i], string + k, 5);
m[i][5] = '\0';
k += 5;
}
for (i = 0 ; i < row ; i++)
{
for (j = 0 ; j < 5 ; j++)
{
m_cfr[i][key[j]] = m[i][j];
}
m_cfr[i][5] = '\0';
printf("%s\n", m_cfr[i]); //--->prints only line i
}
printf("%s\n", m_cfr[0]); //prints whole matrix
strcat(cfr, m_cfr[0]); //concatenates whole matrix
printf("%s\n", cfr);
}
In your code, your array definition is
char m_cfr[row][5];
while you're accessing
m_cfr[i][5] = '\0';
/* ^
|
there is no 6th element
*/
You're facing off-by-one error. Out-of-bound memory access causes undefined behaviour.
Maybe you want to change the null-terminating statement to
m_cfr[i][4] = '\0'; //last one is null
%s expects a char* and prints everything until it encounters a \0. So,
printf("%s\n", m_cfr[i]);
printf("%s\n",m_cfr[0]);
strcat(cfr,m_cfr[0]);
All exhibit Undefined Behavior as m_cfr[i],m_cfr[0] and m_cfr[0] are chars and not char*s and %s as well as both the arguments of strcat expects a char*. Also, as SouravGhosh points out, using
m_cfr[i][5] = '\0';
And
m[i][5] = '\0';
Are wrong.
To fix the former issue, use
printf("%s\n", &m_cfr[i]);
printf("%s\n",m_cfr);
strcat(cfr,&m_cfr[0]);
To print the whole string and concatenate the two strings in the arguments of strcat or if you wanted to print just the chars, use
printf("%c\n", m_cfr[i]);
printf("%c\n",m_cfr[0]);
As for the latter issue, use
char m[row][5]={{0}};
char m_cfr[row][5]={{0}};
Related
Could you help please ?
When I execute this code I receive that:
AAAAABBBBBCCCCCBBBBBCOMP¬ıd┐╔ LENGTH 31
There are some weirds characters after letters, while I've allocate just 21 bytes.
#include <stdio.h>
#include <stdlib.h>
char * lineDown(){
unsigned short state[4] = {0,1,2,1};
char decorationUp[3][5] = {
{"AAAAA"},{"BBBBB"},{"CCCCC"}
};
char * deco = malloc(21);
int k;
int p = 0;
for(int j = 0; j < 4; j++){
k = state[j];
for(int i = 0; i < 5; i++){
*(deco+p) = decorationUp[k][i];
p++;
}
}
return deco;
}
int main(void){
char * lineDOWN = lineDown();
int k = 0;
char c;
do{
c = *(lineDOWN+k);
printf("%c",*(lineDOWN+k));
k++;
}while(c != '\0');
printf("LENGTH %d\n\n",k);
}
The function does not build a string because the result array does not contain the terminating zero though a space for it was reserved when the array was allocated.
char * deco = malloc(21);
So you need to append the array with the terminating zero before exiting the function
//...
*(deco + p ) = '\0';
return deco;
}
Otherwise this do-while loop
do{
c = *(lineDOWN+k);
printf("%c",*(lineDOWN+k));
k++;
}while(c != '\0')
will have undefined behavior.
But even if you will append the array with the terminating zero the loop will count the length of the stored string incorrectly because it will increase the variable k even when the current character is the terminating zero.
Instead you should use a while loop. In this case the declaration of the variable c will be redundant. The loop can look like
while ( *( lineDOWN + k ) )
{
printf("%c",*(lineDOWN+k));
k++;
}
In this case this call
printf("\nLENGTH %d\n\n",k);
^^
will output the correct length of the string equal to 20.
And you should free the allocated memory before exiting the program
free( lineDOWN );
As some other wrote here in their answers that the array decorationUp must be declared like
char decorationUp[3][6] = {
{"AAAAA"},{"BBBBB"},{"CCCCC"}
};
then it is not necessary if you are not going to use elements of the array as strings and you are not using them as strings in your program.
Take into account that your program is full of magic numbers. Such a program is usually error-prone. Instead you should use named constants.
In
char decorationUp[3][5] = {
{"AAAAA"},{"BBBBB"},{"CCCCC"}
};
your string needs 6 characters to also place the null char, even in that case you do not use them as 'standard' string but only array of char. To get into the habit always reverse the place for the ending null character
you can do
char decorationUp[3][6] = {
{"AAAAA"},{"BBBBB"},{"CCCCC"}
};
Note it is useless to give the first size, the compiler counts for you
Because in main you stop when you read the null character you also need to place it in deco at the end, so you need to allocate 21 for it. As before you missed the place for the null character, but here that produces an undefined behavior because you read after the allocated block.
To do *(deco+p) is not readable, do deco[p]
So for instance :
char * lineDown(){
unsigned short state[] = {0,1,2,1};
char decorationUp[][6] = {
{"AAAAA"},{"BBBBB"},{"CCCCC"}
};
char * deco = malloc(4*5 + 1); /* a formula to explain why 21 is better than 21 directly */
int k;
int p = 0;
for(int j = 0; j < 4; j++){
k = state[j];
for(int i = 0; i < 5; i++){
deco[p] = decorationUp[k][i];
p++;
}
}
deco[p] = 0;
return deco;
}
When I print out the length of the temp string, it starts at a random number. The goal of this for loop is to filter out everything that's not a letter, and it works for the most part, but when I print out the filtered string it returns the filtered string but with some extra random characters before and after the string.
#define yes 1000
...
char stringed[yes] = "teststring";
int len = strlen(text);
char filt[yes];
for (int i = 0; i < len; i++) {
if (isalpha(stringed[i])) {
filt[strlen(filt)] = tolower(stringed[i]);
}
}
There are at least two problems with the line:
temp[strlen(temp)] = "\0";
The compiler should be shrieking about converting a pointer to an integer. You need '\0' and not "\0". (This might account for some of the odd characters; the least-significant byte of the address is probably stored over the null byte, making it and random other characters visible until the string printing comes across another null byte somewhere.)
With that fixed, the code carefully writes a null byte over the null byte that marks the end of the string.
You should probably not be using strlen() at this point (or at a number of other points where you use it in the loop).
You should be using i more in the loop. If your goal is to eliminate non-alpha characters, you probably need two indexes, one for 'next character to check' and one for 'next position to overwrite'. After the loop, you need to write over the 'next position to overwrite' with the null byte.
int j = 0; // Next position to overwrite
for (int i = 0; i < length; i++)
{
if (isalpha(text[i]))
temp[j++] = text[i];
}
temp[j] = '\0';
For starters the character array
char temp[MAX];
is not initialized. It has indeterminate values.
So these statements
printf("NUM:[%i] CHAR:[%c] TEMP:[%c] TEMPSTRLEN:[%i]\n", i, text[i], temp[strlen(temp)], strlen(temp));
temp[strlen(temp)] = tolower(text[i]);
have undefined behavior because you may not apply the standard function strlen to uninitialized character array.
This statement
temp[strlen(temp)] = "\0";
is also invalid.
In the left side of the assignment statement there is used the string literal "\0" which is implicitly converted to pointer to its first character.
So these statements
length = strlen(temp);
printf("[%s]\n", temp);
do not make sense.
It seems what you mean is the following
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define MAX 1000
int main(void)
{
char text[MAX] = "teststring";
size_t length = strlen(text);
char temp[MAX] = { '\0' };
// or
//char temp[MAX] = "";
for ( size_t i = 0; i < length; i++)
{
if (isalpha( ( unsigned char )text[i] ) )
{
printf("NUM:[%zu] CHAR:[%c] TEMP:[%c] TEMPSTRLEN:[%zu]\n", i, text[i], temp[strlen(temp)], strlen(temp));
temp[strlen(temp)] = tolower(text[i]);
temp[i+1] = '\0';
}
}
length = strlen(temp);
printf( "[%s]\n", temp );
return 0;
}
The program output is
NUM:[0] CHAR:[t] TEMP:[] TEMPSTRLEN:[0]
NUM:[1] CHAR:[e] TEMP:[] TEMPSTRLEN:[1]
NUM:[2] CHAR:[s] TEMP:[] TEMPSTRLEN:[2]
NUM:[3] CHAR:[t] TEMP:[] TEMPSTRLEN:[3]
NUM:[4] CHAR:[s] TEMP:[] TEMPSTRLEN:[4]
NUM:[5] CHAR:[t] TEMP:[] TEMPSTRLEN:[5]
NUM:[6] CHAR:[r] TEMP:[] TEMPSTRLEN:[6]
NUM:[7] CHAR:[i] TEMP:[] TEMPSTRLEN:[7]
NUM:[8] CHAR:[n] TEMP:[] TEMPSTRLEN:[8]
NUM:[9] CHAR:[g] TEMP:[] TEMPSTRLEN:[9]
[teststring]
Edit: next time do not change your question so cardinally because this can confuse readers of the question.
I'm not sure why malloc is allocating so much space. Here's a snippet of the problem code:
char * hamming_string = NULL;
void enter_params(){
printf("Enter the max length: ");
scanf_s("%d", &max_length);
hamming_string = (char *) malloc(max_length * sizeof(char));
// to test what's going on with the hamming string
for(int i = 0; i < strlen(hamming_string); i++){
hamming_string[i] = 'a';
}
printf("hamming string = %s", hamming_string);
}
I set max_length to 2 and I'm seeing 12 a's. In another function, I was going to have the user input the hamming string using scanf_s("%s", &hamming_string); but I kept getting a access violation
hamming_string is not a string until one of its elements is a '\0'.
The str*() functions can only be used on strings.
Your program invokes Undefined Behaviour (by calling strlen() with something that is not a string).
malloc() allocates the amount of space that you ask for but it does not initialise it. When you call strlen() it scans the memory starting at what hamming_string points to and continues until it finds a null or it accesses memeory that it shouldn't and causes an exception.
In addition you need to allocate space for the null at the end of the string, if you want a string to hold 2 characters you need to allocate 3 characters to allow for the terminating null.
You are asking for the strlen of an uninitialized variable (this is undefined behaviour):
strlen(hamming_string);
(m)allocate one more in order to store the trailling \0:
hamming_string = malloc(max_length + 1);
change to
for(int i = 0; i < max_length; i++){
hamming_string[i] = 'a';
}
and don't forget to add the trailling \0 after the for loop:
hamming_string[i] = '\0'; /* or use calloc and skip this line */
void check_code(){
int actual_length, parity_bit, error_bit = 0, c = 0, i, j, k;
printf("Enter the Hamming code: ");
scanf_s("%s", &hamming_string);
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This scanf_s() call is incorrect.
According to the C11 documentation or MSDN documentation it needs to be
scanf_s("%s", hamming_string, size - 1);
Note that you don't know size inside the function.
Note that you don't pass the address of hamming_string; hamming_string by itself gets converted to the address of its first element.
Example1:
char *hamming_string = malloc((max_length + 1) * sizeof(char));
for (i = 0; i < max_length; i++)
{
hamming_string[i] = 'a';
}
hamming_string[i] = '\0';
printf("hamming string = [%s]\n", hamming_string);
Output:
sdlcb#Goofy-Gen:~/AMD$ ./a.out
hamming string = [aaaaaaaaaaaa]
Example2:
char s;
for (i = 0; i < max_length; i++)
{
scanf(" %c", &s);
hamming_string[i] = s;
}
hamming_string[i] = '\0';
printf("hamming string = [%s]\n", hamming_string);
Output:
sdlcb#Goofy-Gen:~/AMD$ ./a.out
a
b
c
d
e
f
g
h
i
j
k
l
hamming string = [abcdefghijkl]
I am writing a program which will take every 3 numbers in a file and convert them to their ASCII symbol. So I thought I could read the numbers into a character array, and then make every 3 elements 1 element in a second array, convert them to int and then print these as char.
I am stuck on taking every 3 elements, however. This is my code snippet for this part:
char arry[] = "073102109109112"; <--example string read from a file
char arryNew[16] = {0};
for(int i = 0; i <= sizeof(arryNew); i++){
strncpy(arryNew, arry, 3);
arryNew[i+3]='\0';
puts(arryNew);
}
What this code gives me is the first 3 numbers, fifteen times. I've tried incrementing i by 3, which gives me the first 3 numbers 5 times. How do I write a for-loop with strncpy so that after copying n chars, it moves to the next n chars?
You pass always the pointer to the beginning of the array, so you will always have the same result of course. You must include the loop counter to get at the next block:
strncpy(arryNew, &arry[i*3], 3);
Here you have a problem:
arryNew[i+3]='\0';
First of all, you don't need to set the null byte every time, because this will not change anyway. Additionally you will corrupt memory, because you use i+3 as the index so when you reach 14 and 15, it will write beyond the arrayboundary.
Your arrayNew must be longer, because your original array is 16 characters, and your target array is also. If you intend to have several 3char strings in there, then you must have 5*4 characters for your target, because each string also has the 0-byte.
And of course, you must also use the index here as well. The way it is written now, it will write beyond the array boundary, when i reaches 14 and 15.
So what you seem to want to do (not sure from your description) is:
char arry[] = "073102109109112"; <--example string read from a file
char arryNew[20] = {0};
for(int i = 0; i <= sizeof(arry); i++)
{
strncpy(&arryNew[i*4], &arry[i*3], 3);
puts(&arryNew[i*4]);
}
Or if you just want to have the individual strings printed then you can just do:
char arry[] = "073102109109112"; <--example string read from a file
char arryNew[4] = {0};
for(int i = 0; i <= sizeof(arry); i++)
{
strncpy(arryNew, &arry[i*3], 3);
puts(arryNew);
}
Making things a bit simpler: your target string doesn't change.
char arry[] = "073102109109112"; <--example string read from a file
char target[4] = {0};
for(int i = 0; i < strlen(arry) - 3; i+=3)
{
strncpy(target, arry + i, 3);
puts(target);
}
Decoding:
start at the beginning of arry
copy 3 characters to target
(note the fourth element of target is \0)
print out the contents of target
increment i by 3
repeat until you fall off the end of the string.
Some problems.
// Need to change a 3 chars, as text, into an integer.
arryNew[i] = (char) strtol(buf, &endptr, 10);
// char arryNew[16] = {0};
// Overly large.
arryNew[6]
// for(int i = 0; i <= sizeof(arryNew); i++){
// Indexing too far. Should be `i <= (sizeof(arryNew) - 2)` or ...
for (i=0; i<arryNewLen; i++) {
// strncpy(arryNew, arry, 3);
// strncpy() can be used, but we know the length of source and destination,
// simpler to use memcpy()
// strncpy(buf, a, sizeof buf - 1);
memcpy(buf, arry, N);
// arryNew[i+3]='\0';
// Toward the loop's end, code is writing outside arryNew.
// Lets append the `\0` after the for() loop.
// int i
size_t i; // Better to use size_t (or ssize_t) for array index.
Suggestion:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
char Source[] = "073102109109112"; // example string read from a file
const int TIW = 3; // textual integer width
// Avoid sprinkling bare constants about code. Define in 1 place instead.
const char *arry = Source;
size_t arryLen = strlen(arry);
if (arryLen%TIW != 0) return -1; // is it a strange sized arry?
size_t arryNewLen = arryLen/TIW;
char arryNew[arryNewLen + 1];
size_t i;
for (i=0; i<arryNewLen; i++) {
char buf[TIW + 1];
// strncpy(buf, a, sizeof buf - 1);
memcpy(buf, arry, TIW);
buf[TIW] = '\0';
char *endptr; // Useful should OP want to do error checking
// TBD: test if result is 0 to 255
arryNew[i] = (char) strtol(buf, &endptr, 10);
arry += TIW;
}
arryNew[i] = '\0';
puts(arryNew); // prints Ifmmp
return 0;
}
You could use this code to complete your task i.e. to convert the given char array in form of ascii value.
char arry[] = "073102109109112";
char arryNew[16] = {0};
int i,j=0;
for(i = 0; i <= sizeof(arryNew)-2; i+=3)
{
arryNew[j]=arry[i]*100+arry[i+1]*10+arry[i+2]*1;
j++;
arryNew[j+1]='\0';
puts(arryNew);
}
I have a few questions regarding array of strings in C.
I have an array char *string. I have a char *string and then I split every 4 characters in a array of strings called sep_str. So for example if char *string = 'The sum';, then char **sep_str is:
0: |_| --> "The "
1: |_| --> "Sum"
My first question is, in an array of strings in C (so array of array of chars), will there be a null terminating character at the end of each sep_str[i], or just at the last position of sep_str? Here is how I copy string into an array of strings:
for (int i = 0; i < str_length; i++) {
sep_str[i/4][i%4] = *ptr;
ptr++;
}
My second question is, how would I reverse the elements of each string in sep_str? Here's how I did it, but I feel like it is stepping out of the array of the substring. (so out of the element of the sep_str):
// Reverse each element in the array
char temp;
for (int i = 0; i < num_strs; i++) {
for (int j = 0, k = 4; j < k; j++, k--) {
temp = sep_str[i][j];
sep_str[i][j] = sep_str[i][k];
sep_str[i][k] = temp;
}
}
The copy of the strings sounds good to me. Since each string has always 4 chars, you can avoid the null terminator \0. Alternatively you need to declare sep_str as a 5x(lenght/4) matrix, to store the \0 char at the end of each string.
To reverse a string you need to iterate from the start to the middle of the string, replacing the i-th char with the length-i-1-th. You need to replace the inner for replacing k=3 to k=2.
You also need to take care of the last string, since the lenght might not be multiple of four.
char temp;
for (int i = 0; i < (num_strs - 1); i++) {
for (int j = 0, k = 3; j < k; j++, k--) {
temp = sep_str[i][j];
sep_str[i][j] = sep_str[i][k];
sep_str[i][k] = temp;
}
}
if (num_strs > 0) {
for (int j = 0, k = strlen(sep_str[i]) - 1; j < k; j++, k--) {
temp = sep_str[i][j];
sep_str[i][j] = sep_str[i][k];
sep_str[i][k] = temp;
}
}
In a C string, there will be only one termination character. But if you need to tokenize the strings, then each string must be null terminated.
But before that -
char *string = "The sum"; // should be const char* string = "The sum";
String literal in the above case resides in read only location and cannot be modified. If you need to modify, then
char string[] = "The sum";
If you don't have the terminating character in your strings then yes, you will be outside the bounds of the array since you are accessing sep_str[i][4], which is not a valid location:
sep_str[0] = 'T'
sep_str[1] = 'h'
sep_str[2] = 'e'
sep_str[3] = ' '
However, I doubt that you want to have the null character at the beginning of your string, so you need k=3 in your for loop, not k=4.
My first question is, in an array of strings in C (so array of array of chars), will there be a null terminating character at the end of each sep_str[i], or just at the last position of sep_str?
Only at the end, but if you want to treat each individual chunk as its own string, you'll need to add the \0 yourself.
My second question is, how would I reverse the elements of each string in sep_str?
You could do it with pointers...
char temp;
// Point to start of string, `str` will decay to first memory position.
char *start = str;
// Point to the end of the string. You will need to `#include <string.h>`
// for `strlen()`. Otherwise, write a `while` loop that goes until `\0` to find
// the last position.
char *end = &str[strlen(str) - 1];
// Do until we hit the middle of the string.
while (start < end) {
// Need a temp char, no parallel assignment in C.
temp = str[start];
// Swap chars.
str[start++] = str[end];
str[end--] = str[temp];
}
Assuming str is your string.