I've searched around for a quiet some time but surprisingly I couldn't find an answer to it:
I want to rewrite a char array starting from [0], but all what's happening is: it's always appending. Here's my code:
The algorithm is: I have a very long string which I like to break into several lines (wherever there is a blank space at the end of a line). Each line shall be saved in an array Index (lineContent);
void print_text(char* content, int menu_width, int which_selected, int menu_height, int scroll_pos)
{
int posCounter = 0;
int charCounter = menu_width-10;
int printOutCounter;
char* lineContent[400]; // 400 lines max
short spaceFound;
while (strlen(content) > menu_width) // If string is longer than 1 line
{
//Interesting Part ---------- START
char changeString [strlen(content)];
char printString [menu_width-10];
spaceFound = 0;
charCounter = menu_width-10;
lineContent[posCounter] = malloc(MAXITEMSTR);
while (spaceFound == 0)
{
if (content[charCounter] == ' ')
{
// I guess the error goes between here ...
strncpy(changeString,content,strlen(content));
strncpy(printString,content,menu_width-10);
// ...and here
memmove(&changeString[0], &changeString[charCounter], strlen(content));
content=changeString;
lineContent[posCounter]=printString;
strcat(lineContent[posCounter],"\0");
posCounter++;
spaceFound = 1;
//Interesting Part ---------- END
}
charCounter--;
if (charCounter <= 0)
spaceFound = 1;
}
}
}
As I said, in the end, when checking the content of lineContent, every entry is the same (the one from the last line).
I think this is because, strcpy just appends to the end, therefor I have to clear the array, to erase the former line. So it will start from [0] and not from the last printed letter.
Has anybody an idea how to do this? Is there a function that overwrites a char array instead of appending it?
Kind Regards
Strcat appends to the end, strcpy overwrites the value stored in the string.
Related
I have one long array, and I'm trying to figure out how to split it up into two separate arrays, the second array has the right contents but the first is empty, I'm also getting an Abort Trap:6 and I'm not sure what that means.
I have an array called entireA, which looks something like this:
HELLO:WORLD, I want to put HELLO in a separate array (firstA) and WORLD in secondA. When I print first and second array at the end, secondA has the right contents but firstA doesn't event though I'm printing to check if the right characters are being passed over and they are -- but the firstA is still empty and I'm getting and abort trap i don't understand.
I've just started learning C, why is the first array empty and what does the error mean?
#define ARRSIZE 10000
char entireA[ARRSIZE] = "";
char firstA[ARRSIZE] = "";
char secondA[ARRSIZE] = "";
strcpy(entireA,"HELLO:WORLD\n");
int firstVar = 0;
int entireVar = 0;
while(entireA[entireVar] != ':') {
if(entireA[entireVar] == ';') {
break;
}
printf("%c \n",entireA[entireVar]);
firstA[firstVar] = entireA[entireVar];
firstVar++;
entireVar++;
}
firstA[firstVar] = '\0';
int secondVar = 0;
entireVar++; //skip ':'
while(entireA[entireVar] != '\n') {
secondA[secondVar] = entireA[entireVar];
secondVar++;
entireVar++;
}
secondA[secondVar] = '\0';
printf("%s", firstA);
printf("%s", secondA);
There is nothing wrong with the code you posted.
After execution, the variables have the following values:
entireA 0x02efcdb4 "HELLO:WORLD\n" char[0x00002710]
entireVar 0x0000000b int
firstA 0x02efa69c "HELLO" char[0x00002710]
firstVar 0x00000005 int
secondA 0x02ef7f84 "WORLD" char[0x00002710]
secondVar 0x00000005 int
Whatever your problem is, it's most likely something to do with your environment. I would suggest reducing the value of ARRSIZE to, say 80 characters, and seeing if that changes your results.
So I've got this here:
#include <stdio.h>
char halloString[] = "Ha::ll::o";
char perfumeString[] = "47::11";
char veryLongString[] = "47::11::GHesd::dghsr::bfdr:hfgd46dG";
char *extract (char *input) {somethinghappenshere}
where extract needs to get all characters after the last double ":" of given input:
"o" for halloString
"11" for perfumeString
"bfdr:hfgd46dG" for veryLongString
In short, my issue is finding the length of the string *input points to. As far as I understand it that won't be happening without making something really sketchy.
Am I correct in assuming the length cannot be acquired in a good way?
And if so would it be a horrible idea to do, for example:
char stringToProcessTemp1[50];
char stringToProcessTemp2[50];
char stringToProcess[50];
for (int i = 0; i < 50; i++) {
stringToProcessTemp1[i] = input + i;
}
for (int i = 0; i < 50; i++) {
stringToProcessTemp2[i] = input + i;
}
for (int i = 0; i < 50; i++) {
if (stringToProcessTemp1[i] == stringToProcessTemp2[i]) {
stringToProcessTemp[i] = stringToProcessTemp1[i];
}
}
Later checking where the first empty index is and saving everything before it as the used String as from my very limited experience in C when you go outside of an array you tend to get different outputs every time therefore making the chance both Temp strings match for an extra element directly after the last one of the original string what I'd consider low enough.
It's honestly the only idea I've got right now.
Finding the length of a string is no problem. strlen will do that for you. However, you don't even need that.
You can use the strstr function to find a substring within a string, in this case "::". When you find one, keep looking right after the last one you found until you don't find it anymore, then the last one you found is the one you want. Then you want the substring that starts right after it.
char *extract(char *input)
{
char *last = NULL, *start = input, *curr;
while ((curr == strstr(start, "::")) != NULL) {
last = curr; // keep track of the last "::" found
start = last + 1; // move the starting string to right after the last "::"
// move up 1 instead of 2 in case of ":::"
}
if (last != NULL) {
last +=2; // We found one; move just past the "::"
}
return last;
}
C strings, which are really only an array of characters, are by definition terminated by '\0'. So, for a well formed C string you can always get the length of the string by using strlen().
If, however, your string is not null-terminated, there is no way to determine it's length, and it is not a C string by definition any more, but just an array of characters.
Say I have a birthday that is written as 04251993 in some file that
I want to format it as 04/25/1993
I'm assuming that I should make an empty string, or modify the old string into the new string.
I'm not quite sure of how to do that: need some help on writing the function.
I started it out like this.
the first two chars need to be the month with a slash after, 2 more chars with a slash after and then lasty 4 more chars to put out the year.
void timef(char str[]){
printf("%c, str[0]) ?
Make a character array large enough on the heap. Then go through the
characters and insert the slashes. Use fputs to place it in a file. Repeat.
Use "%.*s" to scan the original string and then write to a new one
const char *src = "04251993";
char dest[11];
if (strlen(src) >= 8) {
sprintf(dest, "%.2s/%.2s/%.4s", src, src + 2, src + 4);
}
You can either write a function that is general or one that only performs an operation within set bounds. For this answer, let's just work on the latter. This means, I'll assume your string is always a fixed size of 9 chars (including '\0') and the packing of the data is "mm/dd/yyyy".
From there, you just need to work out how much larger the new string needs to be, and that's originalString + 2 chars, so you need a new array of 11 characters.
char newDate[11] = "";
Then you need to loop through the contents of the original string array and place each character into the new array, as well as adding the slashes as you go. So something like this:
int main()
{
int newSize = 11;
char oldDate[9] = "04231993";
char newDate[11] = "";
for(int i = 0, j = 0; i < newSize && j < oldSize; i++, j++){
if(i == 2){
newDate[i] = '/';
i++;
}
if(i == 5){
newDate[i] = '/';
i++;
}
newDate[i] = oldDate[j];
}
printf("%s", newDate);
}
That's REALLY simple and only to illustrate the basic concept. I would recommend working on your own, more robust version.
I have a char array LL,4014.84954 that I send into a function like this example:
#include <stdio.h>
#include <math.h>
void myFunction(char* in_string, char* out_string) {
printf("Start_String=%s\n", in_string);
int in_size = (int)(sizeof(in_string));
printf("%d\n", in_size);
int i = 0;
for(i = 0; i <= in_size-ceil(in_size/2); i++) {
out_string[i] = in_string[i];
}
}
int main(int arg) {
char in_string[] = "LL,4014.84954";
char out_string[] = "";
printf("In_String=%s\n", in_string);
myFunction(in_string, out_string);
printf("Out_String=%s\n", out_string);
}
My question has two parts.
How do I get the length of this char array? int in_size = (int)(sizeof(in_string)); in this example gives me 8 which is the size of the pointer (long int). I know I could make a for loop that marches through until it see the null termination, but is there a nicer way? I previously was using char[] and sizeof works great, but now I am converting to char*.
How can I write a portion of these chars to out_string. My example currently writes all chars to out_string.
Here is the raw output:
In_String=LL,4014.84954
Start_String=LL,4014.84954
8
Out_String=LL,40014.84954
(1)
Answer to question 2:
char out_string[] = "";
out_string[] is of only one size. you assigning out_string[i] = ... for i > 0 is wrong and cause an undefined error. Instead of this you should declare out_string[] like this:
out_string[] = malloc(strlen(in_string) + 1);
// ^ extra for \0 char
(2)
additionally #WhozCraig commenting correct, you actually need strlen() to find length of string. sizeof you are using wrong.
So replace:
int in_size = (int)(sizeof(in_string));
by
int in_size = strlen(in_string);
(3)
Also, what is in_size-ceil. As I can understands from your raw output you don't need such kind of function and calculations. Just replace your for loop:
for(i = 0; i <= in_size-ceil(in_size/2); i++)
by
for(i = 0; i < in_size; i++)
(4)
At the end don;t forget to terminate you string out_string, after for loop add this line
out_string[i] = '\0'
Regarding your first question, use strlen().
Regarding the second question, first of all you need to make sure that out_string is wide enough to accommodate the result. Currently, it isn't, and the behaviour of your code is undefined. Once you fix that, to copy a portion of the string you'd need to change the initial and final conditions of the for loop, not forgetting about the NUL terminator.
Im working on a project and I am stumped on this part.
I need to read words from stdin and place them in a char array and use an array of pointers to point to each word since they will be jagged. where numwords is an int read in representing the number of words.
char words[10000];
char *wordp[2000];
the problem is that I can only use the pointers to add the words.I can no longer use the [] to help.
*wordp = words; //set the first pointer to the beginning of the char array.
while (t < numwords){
scanf("%s", *(wordp + t)) //this is the part I dont know
wordp = words + charcounter; //charcounter is the num of chars in the prev word
t++;
}
for(int i = 0;words+i != '\n';i++){
charcounter++;
}
any help would be great I am so confused when it comes to pointers and arrays.
Your code will be much more manageable if you use an additional pointer
reference and increment that directly. In this way you won't have to do any
mental math. Additionally you need to be incrementing the reference before
reading in the next string, scanf doesn't move the pointer for you.
char buffer[10000];
char* words[200];
int number_of_words = 200;
int current_words_index = 0;
// This is what we are going to use to write to the buffer
char* current_buffer_prt = buffer;
// quick memset (as I don't remember if c does this for us)
for (int i = 0; i < 10000; i++)
buffer[i] = '\0';
while (current_words_index < number_of_words) {
// Store a pointer to the current word before doing anything to it
words[current_word_index] = current_buffer_ptr;
// Read the word into the buffer
scanf("%s", current_buffer_ptr);
// NOTE: The above line could also be written
// scanf("%s", words[current_word_index]);
// this is how we move the buffer to it's next empty position.
while (current_buffer_ptr != '\n')
current_buffer_ptr++;
// this ensures we don't overwrite the previous \n char
current_buffer_ptr++;
current_words_index += 1;
}
What you want to do is relatively straightforward. You've got an array of 10,000 chars for storage, and 2000 pointers. So to start with you'll want to assign the first pointer to the start of the array:
wordp[0] = &words[0];
In pointer form this is:
*(wordp + 0) = words + 0;
I've used the zeros to show how it relates to the arrays. In general, to set each pointer to each element:
*(wordp + i) == wordp[i]
words + i == &words[i]
So all you need to do is keep track of where you are in the pointer array, and as long as you've assigned correctly, the pointer array will keep track of the position in your char array.