I have a string that has unknown number of float values separated by a white space.(something like this):
12.55 54.11 -1.00000 2.222 ...
Now i need to read all those values into an array.
How do I do this? Do I have to use sscanf?
Do I have to use sscanf?
No, you do not have to, unless you prefer to use it. I would prefer using strtof.
Regardless of the function that you use, you would need to use a loop that reads the values from the string. Since the number of items is unknown, you could scan the string twice - once to learn how many items you have, and a second time to do the actual read. Since the string is in memory, the wasted time in the loop that counts the entries will not be significant.
int cnt = 0;
char *str = "2.55 54.11 -1.00000 2.222";
char *ptr = str, *eptr;
do {
strtof(ptr, &eptr);
ptr = eptr;
cnt++;
} while (*eptr);
printf("%d\n", cnt);
float *res = malloc(cnt*sizeof(float));
ptr = str;
for (int i = 0 ; i != cnt ; i++) {
res[i] = strtof(ptr, &eptr);
ptr = eptr;
}
for (int i = 0 ; i != cnt ; i++) {
printf("%f\n", res[i]);
}
Demo on ideone.
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;
}
I have to write a function that finds a product with given code from the given array. If product is found, a pointer to the corresponding array element is returned.
My main problem is that the given code should first be truncated to seven characters and only after that compared with array elements.
Would greatly appreciate your help.
struct product *find_product(struct product_array *pa, const char *code)
{
char *temp;
int i = 0;
while (*code) {
temp[i] = (*code);
code++;
i++;
if (i == 7)
break;
}
temp[i] = '\0';
for (int j = 0; j < pa->count; j++)
if (pa->arr[j].code == temp[i])
return &(pa->arr[j]);
}
Why don't you just use strncmp in a loop?
struct product *find_product(struct product_array *pa, const char *code)
{
for (size_t i = 0; i < pa->count; ++i)
{
if (strncmp(pa->arr[i].code, code, 7) == 0)
return &pa->arr[i];
}
return 0;
}
temp is a pointer which is uninitialized and you are dereferencing it which will lead to undefined behavior.
temp = malloc(size); // Allocate some memory size = 8 in your case
One more mistake I see is
if (pa->arr[j].code == temp[i]) // i is already indexing `\0`
should be
strcmp(pa->arr[j].code,temp); // returns 0 if both the strings are same
This code can completely be avoided if you can use strncmp()
As pointed out by others, you are using temp uninitialized and you are always comparing characters with '\0'.
You don't need a temp variable:
int strncmp ( const char * str1, const char * str2, size_t num );
Compare characters of two strings
Compares up to num characters of the
C string str1 to those of the C string str2.
/* Don't use magic numbers like 7 in the body of function */
#define PRODUCT_CODE_LEN 7
struct product *find_product(struct product_array *pa, const char *code)
{
for (int i = 0; i < pa->count; i++) {
if (strncmp(pa->arr[i].code, code, PRODUCT_CODE_LEN) == 0)
return &(pa->arr[i]);
}
return NULL; /* Not found */
}
When you write char* temp; you are just declaring an uninitialized pointer
In your case since you say that the code is truncated to 7 you could create a buffer
on the stack with place for the code
char temp[8];
Writing
temp[i] = (*code);
code++;
i++;
Can be simplified to:
temp[i++] = *code++;
In your loop
for (int j = 0; j < pa->count; j++)
if (pa->arr[j].code == temp[i])
return &(pa->arr[j]);
You are comparing the address of code and the character value of temp[i] which incidentally could be 8 and outside the array.
Instead what you want to do is compare what code points to and what temp contains:
for (int j = 0; j < pa->count; j++)
if (!strncmp(pa->arr[j].code, temp, 7)
return &(pa->arr[j]);
You should also return NULL; if nothing was found, seems you do not return anything.
Probably a good thing is also to make sure your temp[] always contains 7 characters.
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'd like to fill a char-array dynamically and check whether the contained values are valid integers, here's what I got so far:
for(int i = 0; i < 50000; i++)
{
if(input[i] == ',')
{
commaIndex = i;
}
}
commaIndex is the index of a comma inside a file, numerical values should have been entered before a comma, file looks like this: -44,5,19,-3,13,(etc), it's important for this part:
char *tempNumber = new char[commaIndex];
Fill tempNumber (which should presumably be just as big as the number due to my dynamic allocation) so I don't have a number in a size 50000 char-array (named input).
for(int i = 0; i < commaIndex; i++)
{
cout << i << "\n";
tempNumber[i] = input[i];
}
And now I want to use it:
if(!isValidInteger(tempNumber))
{
cout << "ERROR!\n";
}
Unfortunately, tempNumber always seems to be of size 4 irregardless of the value of "commaIndex", i.e. I get the following output:
(Inputdata: 50000,3,-4)
commaIndex: 5
content of tempNumber: 5000 (one 0 missing)
commaIndex: 1
content of tempNumber: 3²²² (notice the 3 ^2s)
commaIndex: 2
content of tempNumber: -4²²
Any ideas?
One more thing: This is for a homework assignment and I am not allowed to use any object-oriented element of C++ (this includes strings and vectors, I've been there and I know it would be SO easy.)
Thanks,
Dennis
You might be interested by the strtol function.
You may also consider using strtok() with sscanf(). Notice, that strtol() does not allow you to check for errors since it simply returns (perfectly valid) value 0 on parse error. On the other hand, sscanf() returns number of successfully read items, so you may easily check if there was an error while reading a number.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
int i = 0;
char str[] = "1,2,-3,+4,a6,6";
/* calculate result table size and alloc */
int max = 1;
char* tmp = str;
while (*tmp)
if (*tmp++ == ',')
++max;
int* nums = malloc(sizeof(int) * max);
/* tokenize string by , and extract numbers */
char* pch = strtok(str, ",");
while (pch != NULL) {
if (sscanf(pch, "%d", &nums[i++]) == 0)
printf("Not a number: %s\n", pch);
pch = strtok(NULL, ",");
}
/* print read numbers */
for (i = 0; i < max; ++i)
printf("%d\n", nums[i]);
free(nums);
return 0;
}
Trying to use as basic C as I can to build a list of numbers from 1-52 in a random order (deck of cards). Everything works, but all of my attempts to concat the strings and get a result end in failure. Any suggestions? NOTE: This is not homework it's something I'm using to create a game.
// Locals
char result[200] = ""; // Result
int card[52]; // Array of cards
srand(time(0)); // Initialize seed "randomly"
// Build
for (int i=0; i<52; i++) {
card[i] = i; // fill the array in order
}
// Shuffle cards
for (int i=0; i<(52-1); i++) {
int r = i + (rand() % (52-i));
int temp = card[i]; card[i] = card[r]; card[r] = temp;
}
// Build result
for (int c=0; c<52; c++) {
// Build
sprintf(result, "%s%d", result, card[c]);
// Comma?
if ( c < 51 )
{
sprintf(result, "%s%s", result, ",");
}
}
My end result is always garbled text. Thanks for the help.
You keep writing to the same position of "result".
sprintf is not going to do the appending for you.
You may consider, after each sprintf, get the return value (which is the number of char written), and increment the pointer to result buffer. i.e. something like:
(psuedo code):
char result[200];
char * outputPtr = result;
for (int c=0; c<52; c++) {
// Build
int n = sprintf(outputPtr, "%d%s", card[c], (c<51 ? "," : ""));
outputPtr += n;
}
Are we writing C++ or C? In C++, concat-ing a string is just:
string_out = string_a + string_b
…since you'd be using std::string.
Furthermore, if this is C++, the STL has a std::shuffle function.
If this is C, note that all your sprintfs aren't concatenating strings, they're just overwriting the old value.
I think, if memory serves, that sprintf will always write into the buffer starting at byte 0. This means that you would be writing the first couple of bytes over and over again with a number, then a comma, then a number. Check if your first bytes are ",[0-9]" - if so, that's your issue.
This would add a comma between each number in the result string:
// Get a pointer to the result string
char* ptr = &result[0];
for (int c = 0; c < 52; c++) {
// Add each cards number and increment the pointer to next position
ptr += sprintf(ptr, "%d", card[c]);
// Add a separator between each number
if (c < 51) {
*ptr++ = ',';
}
}
// Make sure the result string is null-terminated
*ptr = 0;