I have a linux box.
On this linux box, there is a program.
In this program, I have a loop like this:
int num=*"what num needs to be"*;
char proc[num];
int result;
while (1) {
result=scanf("%[^'&']%s",proc);
printf("And proc is: %s\n",proc);
printf("Result counter was: %i\n",result)
if (result == 0) break;
}
scanf("%[^'&'],%s",proc)
printf("post lop result is: %s", proc);
As you may have guessed, stdin contains data I need delineated by the '&' character.
As I'm hoping someone more skilled than me has guessed, the output looks something like:
And proc is: *first delineated section*
Result counter was: 1
And proc is: *first delineated section*
Result counter was: 0
post loop result is: *first delineated section*
I thought that scanf was supposed to consume the part of stdin it has already read. Why isn't it doing this?
Also, FYI: this is being run on a very cheap, slow server. Volume may or may not become more than slight. Efficiency is thus a plus, I'm open to however someone might suggest I do this....
Thanks!
The scanset does not need two single quotes in it — one is sufficient if you want to break on a single quote, but I suspect you only want to stop on &, and the code below assumes that too. Once you've read up to the first &, you need some code to read the &. You need to check the result of scanf() before using the data it returned.
Hence:
int num = 100;
char proc[num];
int result;
while ((result = scanf("%99[^&]", proc)) == 1)
{
printf("And proc is: <<%s>>\n", proc);
printf("Result counter was: %i\n", result);
int c;
while ((c = getchar()) != EOF && c != '&')
;
}
You also need to decide whether newlines mark the end of a field too...if they do, then:
int num = 100;
char proc[num];
int result;
while ((result = scanf("%99[^&\n]", proc)) == 1)
{
printf("And proc is: <<%s>>\n", proc);
printf("Result counter was: %i\n", result);
int c;
while ((c = getchar()) != EOF)
{
if (c != '&' && c != '\n')
{
ungetc(c, stdin);
break;
}
}
}
Note the use of %99[...] to prevent buffer overflows. The angle brackets <<%s>> simply mark the start and end of the string; they make trailing blanks and tabs visible, for example.
The code assumes you have a C99 compiler that allows variable declarations midway through a block of code. If not, move int c; to the top of the loop
The problem is that on the second iteration the scanf can't read the format you gave it (the line read from standard input does not match) and doesn't modify proc. That's also the reason it returns 0: it has successfully read (and thus modified) 0 fields.
Related
Input : [1,3,2,4]
I want to make arr[4] = {1, 3, 2, 4} from this input using scanf(). How can I do this in C language?
It is possible to parse input such as you describe with scanf, but each scanf call will parse up to a maximum number of fields determined by the given format. Thus, to parse an arbitrary number of fields requires an arbitrary number of scanf calls.
In comments, you wrote that
I want to find a method to ignore '[', ']', ',' and only accept integer units.
Taking that as the focus of the question, and therefore ignoring the issues of how you allocate space for the integers to be read when you do not know in advance how many there will be, and assuming that you may not use input functions other than scanf, it seems like you are looking for something along these lines:
int value;
char delim[2] = { 0 };
// Scan and confirm the opening '['
value = 0;
if (scanf("[%n", &value) == EOF) {
// handle end of file or I/O error ...
} else if (value == 0) {
// handle input not starting with a '[' ...
// Note: value == zero because we set it so, and the %n directive went unprocessed
} else {
// if value != 0 then it's because a '[' was scanned and the %n was processed
assert(value == 1);
}
// scan the list items
do {
// One integer plus trailing delimiter, either ',' or ']'
switch(scanf("%d%1[],]", &value, delim)) {
case EOF:
// handle end of file or I/O error (before an integer is read) ...
break;
case 0:
// handle input not starting with an integer ...
// The input may be malformed, but this point will also be reached for an empty list
break;
case 1:
// handle malformed input starting with an integer (which has been scanned) ...
break;
case 2:
// handle valid (to this point) input. The scanned value needs to be stored somewhere ...
break;
default:
// cannot happen
assert(0);
}
// *delim contains the trailing delimiter that was scanned
} while (*delim == ',');
// assuming normal termination of the loop:
assert(*delim == ']');
Points to note:
it is essential to pay attention to the return value of scanf. Failure to do so and to respond appropriately will cause all manner of problems when unexpected input is presented.
the above will accept slightly more general input than you describe, with whitespace (including line terminators) permitted before each integer.
The directive %1[],] attempts to scan a 1-character string whose element is either ] or ,. This is a bit arcane. Also, because the input is scanned as a string, you must be sure to provide space for a string terminator to be written, too.
it would be easier to write a character-by-character parser for your specific format that does not rely on scanf. You could also use scanf to read one character at a time to feed such a parser, but that seems to violate the spirit of the exercise.
While I think that John Bollinger answer is pretty good and complete (even without considering the wonderful %1[[,]), I would go for a more compact and tolerant version like this:
#include <stdio.h>
size_t arr_input(int *arr, size_t max_size)
{
size_t n;
for (n = 0; n < max_size; ++n) {
char c;
int res = scanf("%c%d", &c, arr + n);
if (res != 2
|| (n == 0 && c != '[')
|| (n > 0 && c != ',')
|| (n > 0 && c == ']')) {
break;
}
}
return n;
}
int main(void)
{
char *test_strings[] = { "[1,2,3,4]", "[42]", "[1,1,2,3,5,8]", "[]",
"[10,20,30,40,50,60,70,80,90,100]", "[1,2,3]4" };
size_t test_strings_n = sizeof test_strings / sizeof *test_strings;
char filename[L_tmpnam];
tmpnam(filename);
for (size_t i = 0; i < test_strings_n; ++i) {
freopen(filename, "w+", stdin);
fputs(test_strings[i], stdin);
rewind(stdin);
int arr[9];
size_t num_elem = arr_input(arr, 9);
printf("%zu: %s -> ", i, test_strings[i]);
for (size_t j = 0; j < num_elem; ++j) {
printf("%d ", arr[j]);
}
printf("\n");
fclose(stdin);
}
remove(filename);
return 0;
}
The idea is that you allocate space for the maximum number of integers you accept, then ask the arr_input() function to fill it up to max_size elements.
The check after scanf() tries to cope with incorrect input, but is not very complete. If you trust your input to be correct (don't) you can even make it shorter, by dropping the three || cases.
The most complex thing was to write the test driver with tmp files, strings, reopening and such. Here I'd have loved to have std::istream to just drop a std::stringstream. The fact that the FILE interface doesn't support strings really bugs me.
int arr[4];
for(int i=0;i<4;i++) scanf("%d",&arr[i]);
Are you asking for this? I was little bit confused with your question, if this doesn't solve your query, then don't hesitate to ask again...
use scanf to read a string input from user then parse that input into an integer array
To parse you can use string function "find" to locate the "," and "[]" and then use "atoi" to convert string into integer to fill the destination input array.
Edit: find is a C++ function.
the C function is strchr
I have a text file that looks like the following:
12345678909876543211234567890
09876543122345678900
I will eventually need to add these two values together using separate stacks so I want to push each digit into a stack separately so I have code like the following:
test=fopen("test.txt","r");
while (!feof(fp)) {
fscanf(test, "%1d", &number);
Push((Item)number, &num1);
}
I need to modify my code though so that it reads the first line 1 digit at a time, pushing on each digit, and then for the next line I need it to push into another stack called num2 instead of num1 as you see in the current code.
You've not told us about the stack types, so I'm inventing one — typedef name is Stack:
Stack num1, num2;
Stack *stacks[2] = { &num1, &num2 };
…initialize stacks
…open file and check that the open was successful
for (int i = 0; i < 2; i++)
{
char line[4096];
if (fgets(line, sizeof(line), test) == 0)
…report unexpected EOF or other error; do not continue…
char *digit = line;
while (isdigit((unsigned char)*digit))
Push((Item)(*digit++ - '0'), stacks[i]);
if (*digit != '\n' && *digit != '\0')
…report unexpected (non-digit) data on input; do not continue;
}
I assume that Push is a function, not a macro that might evaluate its first argument more than once. If it is such a macro, the loop body needs be split onto two lines and braces added so that the increment of digit is separate from the function call.
Note that one major advantage of this method is that you have the whole line of data available for error reporting, which is typically easier for people to understand than only being able to report on the dribs and drabs left over after a semi-indeterminate number of characters was read from the line by a scanf() loop. You can even use sscanf() on the line if you want to — see How to use sscanf() in loops?
I am previously a java programmer, but I'm now doing a C course at university (computer science major).
I need the user to be able to enter 3 chars,the first 2 being numbers, and the last 1 being either 'v' or 'h'.
For example "1 2 v".
I need the user to be able to enter it with the spaces in between each character.
This is my current code:
void manageInput(char box[][width]){
char move[4];
char input[16];
while(1){
scanf("%s", input);
int i = 0;
while(input[i] != 0){
if(input[i] != ' ' && input[i] != "\n"){
move[i] = input[i];
}
i++;
}
printf("%s\n", move);
makeMove(box, move);
printBox(box, height, width);
// TODO
if(move[0] == 'x'){
exit(0);
}
}
}
However if I run it, it works fine when I enter the chars with out spaces like "12v", but If I enter "1 2 v", it will print out "1", call printBox, then print out "2", then print out box again, and so on.
If someone could explain what I'm doing wrong here, I would appreciate it.
If someone could explain what I'm doing wrong here, I would appreciate it.
The short story is: Your code doesn't fulfill your requirements. It simply doesn't do what you want it to do.
Your requirements are:
All fields must be one character. This requirement isn't fulfilled by your code. Your code will mistakenly accept multiple characters per field.
There must be one space (exactly one space?) between the fields. This requirement isn't fulfilled by your code. There might be multiple spaces between the fields, and your code will mistakenly accept that.
In fact, your code invokes undefined behaviour by accessing the move array out of bounds. Consider that as a consequence of one of the above scenarios i might become some value higher than 3. What might happen in this code: move[i] = input[i];?
Your code is also way too complex. All of your functionality can be performed by scanf alone. It's a very powerful function, when you know how to use it correctly... I suggest reading and understanding the manual multiple times, when you have an opportunity. You'll learn a lot!
I notice something you neglected to mention from within the logic you have presented: It's expected that the first field might also be 'x', which corresponds to an exit usecase. This is a bad design; the caller has no opportunity to clean up... but I'll run with it. You really should use return (and return an int value or something, corresponding to error/success) instead.
Let us caste that last paragraph aside, because we can simply consider 'x' to be invalid input (and exit as a result), and I don't want to change the contracts of your functions; I'll leave that to you. The expression described so far appears to be int x = scanf("%1[0123456789]%*1[ ]%1[0123456789]%*1[ ]%1[vh]", a, b, c);.
Note that it is expected that a, b and c will have enough space to store a string of one byte in length. That is, their declaration should look like: char a[2], b[2], c[2];.
Make sure you check the return value (x, in the example)! If x is 3, it's safe to assume that the three variables a, b and c are safe to use. If x is 2, it's safe to assume that a and b are safe to use, and so on... If x is EOF or 0, none of them are safe to use.
By checking the return value, you can reject input that doesn't match that precise pattern, that is:
Fields that aren't exactly one byte in width will be rejected.
Too many or too few spaces will be rejected.
Something else popped up that you have neglected to mention, and it's also present within your code: Chux mentioned that you'll likely be expecting the input to be terminated with a '\n' (newline) character. This can also be implemented in a number of ways using scanf:
scanf("%1*[\n]"); will attempt to read and discard precisely one '\n' character, but there's no way to ensure that was successful. getchar would be more appropriate for that purpose; something along the lines of if (getchar() != '\n') { exit(EXIT_FAILURE); } might make sense, if you wish to ensure that the lines of input are perfectly formed and bomb out when they aren't... #define BOMB_OUT?
scanf("%*[^\n]"); scanf("%*c"); makes more sense; If you're interested in reading one item per line, then it makes sense to discard everything remaining on the line, and then the newline character itself. Note that your program should always tell the user when it's discarding or truncating input. You could also use getchar for this.
void manageInput(char box[][width]){
for (;;) {
char a[2], b[2], c[2];
int x = scanf("%1[0123456789]%*1[ ]%1[0123456789]%*1[ ]%1[vh]", a, b, c);
if (x != 3) {
/* INVALID INPUT should cause an error value to be returned!
* However, this function has no return value (which makes it
* poorly designed)... Calling `exit` gives no opportunity for
* calling code to clean up :(
*/
exit(EXIT_FAILURE);
}
if (getchar() != '\n') {
# ifdef BOMB_OUT
exit(EXIT_FAILURE);
# else
scanf("%*[^\n]");
getchar();
puts("NOTE: Excess input has been discarded.");
# endif
}
char move[4] = { a[0], b[0], c[0] };
printf("%s\n", move);
makeMove(box, move);
printBox(box, height, width);
// TODO
if(move[0] == 'x'){
exit(0);
}
}
}
%s reads a whitespace-delimited string with scanf, so if that's not what you want, it's not the thing to use. %c reads a single character, but does not skip whitespce, so you probably also want a (space) in your format to skip whitespace:
char input[3];
scanf(" %c %c %c", intput, input+1, input+2);
will read 3 non-whitespace characters and skip any whitespace before or between them. You should also check the return value of scanf to make sure that it is 3 -- if not, there was less than 3 characters in your input before an end-of-file was reached.
It's usuall a bad idea to read string via scanf because of potential buffer overflow. Consider using fscanf or better fgets as in
fgets(input, 15, stdin);
Note the extra byte for '\0'.
Also, you're comparing char to string here: input[i] != "\n". It should be input[i] != '\n' instead.
And btw you can just use something like
int x, y;
char d;
scanf("%d%d%c", &x, &y, &d);
This looks like two simple bugs.
You need to use separate indexes for move[] and input[]
int i = 0;
while(input[i] != 0){
if(input[i] != ' ' && input[i] != "\n"){
move[i] = input[i];
}
i++;
}
Imagine input of 1 2 v
input[0] != 0, so we enter the loop
it's not ' ' or '\n' either, so we copy input[0] to move[0]
so far so good
You increment i, and discover that input[1] == ' '
But then you increment i again
You discover that you are interested in input[2] (2) - so you copy it to move[2], rather than move[1]. Oops!
Then to make things worse, you never put an end-of-string character after the last valid character of move[].
So I'm trying to get the number of lines in a text file of words each on a new line. I have this method so far...
char * getS(char *fileName){
FILE *src;
if((src = fopen(fileName, "r")) == NULL){
printf("%s %s %s", "Cannot open file ", fileName, ". The program is now ending.");
exit(-1);
}
char *get = ".";
int c = 0;
char ch = 'x';
while(ch!=EOF) {
ch = fgetc(src);
if(ch == '\n') c++;
}
fseek(src, 0, SEEK_SET);
printf("%i",c);
int random = rand() % (c - 1);
return get;
}
For some reason if I put a printf for ch in the middle of the while it will give me the correct number of lines, otherwise it 7801729.
Also how would I make a random int from 0 to the number of lines? The concept of using random in C is rather baffling to me right now.
Thanks in Advance!
I think fgetc() returns an int but you are stuffing the returned value into a char (without casting it to a char) so you're getting the first byte of the returned int in the right place (in your ch variable) but the additional three bytes overflow into your c variable, which is defined adjacent to ch on the stack. When you increment c, it's increasing the first byte (which suggests you're on a big-endian machine) but those extra three bytes in your int are untouched and left corrupted by the overwrite from the getc() return. That's why the first byte in your answer looks correct. Try defining ch as an int and I bet your problem goes away (though you might have to add some casting to avoid compiler errors/warnings).
I have the following in a text file called: values.txt
1 4
2.5 3.76
122 10
277.543
165.4432
I am trying to read the content of this text file, and add each two pairs together and output the result ...
the output would be something like this :
1 Pair:(1, 4) = 5
2 Pair:(2.5, 3.76)= 6.26
and so on ..
I am opening the file like this
int c;
FILE myfile;
myfile= fopen("values.txt", "r");
if ( myfile == NULL ) {
printf("Cannot open TEXT file\n");
return 1;
}
double aa,bb;
while ( (c = getc(myfile) ) != EOF ) {
// HERE SHOULD I DO THE OUTPUT BUT HOW?
}
Any help is really appreciated ..
Language = C
The following code does what you expect. myfile should be declared as FILE*. fopen returns a pointer to FILE structure. If the file is very large, I would recommend reading in buffers of big size (eg: 65535 etc) and parse it char by char and convert it to float values. It reduces system call overhead which takes more time than processing text to float values.
#include <stdio.h>
#include <string.h>
main(int argc, char *argv[])
{
FILE* myfile;
myfile = fopen("values.txt", "r");
if ( myfile == NULL ) {
printf("Cannot open TEXT file\n");
return 1;
}
double aa,bb;
while (2 == fscanf(myfile, "%lf %lf", &aa, &bb)) {
printf("%lf\n", aa+bb);
}
return 0;
}
For this simple task, use double a, b;
if (fscanf(myfile, "%lf %lf", &a, &b) == 2)
printf("%f + %f = %f\n", a, b, a+b);.
looks like a homework problem but fscanf can read the string into a variable like:
int n;
fscanf (myfile,"%d",&n);
You haven't shown what you need as output for the single-value lines, but this looks like a case for fgets() and sscanf(), unless you really want the two lines with a single value to be processed as a unit.
char buffer[256];
int rownum = 0;
while (fgets(buffer, sizeof(buffer), myfile) != 0)
{
double aa, bb;
int n = sscanf(buffer, "%lf %lf", &aa, &bb);
if (n == 2)
printf("%d Pair:(%g, %g) = %g\n", ++rownum, aa, bb, aa+bb);
else if (n == 1)
printf("%d Solo:(%g) = %g\n", ++rownum, aa, aa);
else
{
printf("Failed to find any numbers in <<%s>>\n", buffer);
}
}
If you used fscanf(myfile, "%g %g", &aa, &bb), then it would read over newlines (they count as white space) looking for numbers, so it would read one number from one line, and the second from another line. This is not usually what people are after (but when it is what you need, it is extremely useful). Error recovery with fscanf() tends to be more fraught than with fgets() and sscanf().
its in c++ sorry :( i dont know c
this is a very simple logic code for simple minde :D im a begineer too, i havent tested this prog so sorry if something goes wrong but exactly
on a same principle was working my parser and it worked fine. so this is a true method. not very efficent but...
do not use this program straight away, understand it's logic this will help you alot. copying that wont give you anything
...parser tutors are so rare....
int x=0;
char ch = 'r'; //i'v used this equasion to avoid error on first ckeck of ch.
it must be filled by something when program starts.
char bigch[10];
int checknumber = 0;
float firstnumber = 0;
float secondnumber = 0;
float result=0;
void clearar(char frombigar[10], int xar) //this function gets bigch as a reference which means that eny
changes made here, will directly affect bigch itself.
ths function gets the actual length of array and puts spaces
in bigch's every element to zero out numbers. we need to clear
bigch of any previous numbers. down below you'l see why i needed this.
'xar' is the x from main function. its here to tell our cleaner the
true length of filled bigar elements.
{
for (int i=0; i
}
}
int main()
{
<------------------- //here you add file opening and reading commands
while(!myfile.eof()) //while end of txt file have not been reached
{
ch=myfile.get(); //gets each letter into ch, and make cursor one step
forward in txt file for further reading.
get() does cursor forwarding automatically
if (ch!= " ") //i used space as an indicator where one number ends
//so while space havent been reahced, read letters.
{ bigch[x] = ch; //get read letter into bigch array.
x++; //icrement bigch array step
}
else
if(ch == " ") //if space is reached that means one number has ended and
{ im trying to set a flag at that moment. it will be used further.
checknumber++; the flag is simple number. first space will set checknumber to 1
second space will set it to 2. thats all.
}
if (checknumber == 1) //if our checknumber is 1, wich means that reading
of first number is done, lets make one whole float
from that bigch array.
{ firstnumber = atof(bigch); //here we get bigch, atof (array to float) command converts
bigch array into one whole float number.
clearar(bigch,x); //here we send bigch and its element step into function where
bigch gets cleaned because we dont want some ghost numbers in it.
abviously clearar function cleans bigch int main function aswell,
not only in it's teritory. its a global cleaning :)
}
else if (checknumber ==2) //here we do the same but if flag is 2 this means that two spaces
had been passed and its time to convert bigch into secondnumber.
{ secondnumber = atof(bigch); //same method of converting array into float (it hates other
not number letters, i mean if its a number its fine. if in your text
was 'a' or 's' in that case atof will panic hehe.. )
clearar(bigch,x); //same thing, we send bigch to cleaner function to kill any numbers
it, we get one space letter ( " " ) into each element of bigch.
}
checknumber = 0; if both two numbers had been read out and converted. we need to reset
space flagger. and start counting form 0; for next pair numbers.
result = firstnumber+secondnumber; well here everything is clear.
}
}