I was trying to take a full line input in C. Initially I did,
char line[100] // assume no line is longer than 100 letters.
scanf("%s", line);
Ignoring security flaws and buffer overflows, I knew this could never take more than a word input. I modified it again,
scanf("[^\n]", line);
This, of course, couldn't take more than a line of input. The following code, however was running into infinite loop,
while(fscanf(stdin, "%[^\n]", line) != EOF)
{
printf("%s\n", line);
}
This was because, the \n was never consumed, and would repeatedly stop at the same point and had the same value in line. So I rewrote the code as,
while(fscanf(stdin, "%[^\n]\n", line) != EOF)
{
printf("%s\n", line);
}
This code worked impeccably(or so I thought), for input from a file. But for input from stdin, this produced cryptic, weird, inarticulate behavior. Only after second line was input, the first line would print. I'm unable to understand what is really happening.
All I am doing is this. Note down the string until you encounter a \n, store it in line and then consume the \n from the input buffer. Now print this line and get ready for next line from the input. Or am I being misled?
At the time of posting this question however, I found a better alternative,
while(fscanf(stdin, "%[^\n]%*c", line) != EOF)
{
printf("%s\n", line);
}
This works flawlessly for all cases. But my question still remains. How come this code,
while(fscanf(stdin, "%[^\n]\n", line) != EOF)
{
printf("%s\n", line);
}
worked for inputs from file, but is causing issues for input from standard input?
Use fgets(). #FredK
char buf[N];
while (fgets(buf, sizeof buf, stdin)) {
// crop potential \n if desired.
buf[strcspn(buf, "\n")] = '\0';
...
}
There are to many issues trying to use scanf() for user input that render it prone to mis-use or code attacks.
// Leaves trailing \n in stdin
scanf("%[^\n]", line)
// Does nothing if line begins with \n. \n remains in stdin
// As return value not checked, use of line may be UB.
// If some text read, consumes \n and then all following whitespace: ' ' \n \t etc.
// Then does not return until a non-white-space is entered.
// As stdin is usually buffered, this implies 2 lines of user input.
// Fails to limit input.
scanf("%[^\n]\n", line)
// Does nothing if line begins with \n. \n remains in stdin
// Consumes 1 char after `line`, even if next character is not a \n
scanf("%99[^\n]%*c", line)
Check against EOF is usual the wrong check. #Weather Vane The following, when \n is first entered, returns 0 as line is not populated. As 0 != EOF, code goes on to use an uninitialized line leading to UB.
while(fscanf(stdin, "%[^\n]%*c", line) != EOF)
Consider entering "1234\n" to the following. Likely infinite loop as first fscanf() read "123", tosses the "4" and the next fscanf() call gets stuck on \n.
while(fscanf(stdin, "%3[^\n]%*c", line) != EOF)
When checking the results of *scanf(), check against what you want, not against one of the values you do not want. (But even the following has other troubles)
while(fscanf(stdin, "%[^\n]%*c", line) == 1)
About the closest scanf() to read a line:
char buf[100];
buf[0] = 0;
int cnt = scanf("%99[^\n]", buf);
if (cnt == EOF) Handle_EndOfFile();
// Consume \n if next stdin char is a \n
scanf("%*1[\n]");
// Use buf;
while(fscanf(stdin, "%[^\n]%*c", line) != EOF)
worked for inputs from file, but is causing issues for input from standard input?
Posting sample code and input/data file would be useful. With modest amount of code posted, some potential reasons.
line overrun is UB
Input begins with \n leading to UB
File or stdin not both opened in same mode. \r not translated in one.
Note: The following fails when a line is 100 characters. So meeting the assumption cal still lead to UB.
char line[100] // assume no line is longer than 100 letters.
scanf("%s", line);
Personally, I think fgets() is badly designed. When I read a line, I want to read it in whole regardless of its length (except filling up all RAM). fgets() can't do that in one go. If there is a long line, you have to manually run it multiple times until it reaches the newline. The glibc-specific getline() is more convenient in this regard. Here is a function that mimics GNU's getline():
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
long my_getline(char **buf, long *m_buf, FILE *fp)
{
long tot = 0, max = 0;
char *p;
if (*m_buf == 0) { // empty buffer; allocate
*m_buf = 16; // initial size; could be larger
*buf = (char*)malloc(*m_buf); // FIXME: check NULL
}
for (p = *buf, max = *m_buf;;) {
long l, old_m;
if (fgets(p, max, fp) == NULL)
return tot? tot : EOF; // reach end-of-file
for (l = 0; l < max; ++l)
if (p[l] == '\n') break;
if (l < max) { // a complete line
tot += l, p[l] = 0;
break;
}
old_m = *m_buf;
*m_buf <<= 1; // incomplete line; double the buffer
*buf = (char*)realloc(*buf, *m_buf); // check NULL
max = (*m_buf) - old_m;
p = (*buf) + old_m - 1; // point to the end of partial line
}
return tot;
}
int main(int argc, char *argv[])
{
long l, m_buf = 0;
char *buf = 0;
while ((l = my_getline(&buf, &m_buf, stdin)) != EOF)
puts(buf);
free(buf);
return 0;
}
I usually use my own readline() function. I wrote this my_getline() a moment ago. It has not been thoroughly tested. Please use with caution.
Related
How to accept set of strings as input in C and prompt the user again to re-enter the string if it exceeds certain length. I tried as below
#include<stdio.h>
int main()
{
char arr[10][25]; //maximum 10 strings can be taken as input of max length 25
for(int i=0;i<10;i=i+1)
{
printf("Enter string %d:",i+1);
fgets(arr[i],25,stdin);
}
}
But here fgets accepts the strings greater than that length too.
If the user hits return, the second string must be taken as input. I'm new to C
How to accept string input only if it of certain length
Form a helper function to handle the various edge cases.
Use fgets(), then drop the potential '\n' (which fgets() retains) and detect long inputs.
Some untested code to give OP an idea:
#include <assert.h>
#include <stdio.h>
// Pass in the max string _size_.
// Return NULL on end-of-file without input.
// Return NULL on input error.
// Otherwise return the buffer pointer.
char* getsizedline(size_t sz, char *buf, const char *reprompt) {
assert(sz > 0 && sz <= INT_MAX && buf != NULL); // #1
while (fgets(buf, (int) sz, stdin)) {
size_t len = strlen(buf);
// Lop off potential \n
if (len > 0 && buf[--len] == '\n') { // #2
buf[len] = '\0';
return buf;
}
// OK if next ends the line
int ch = fgetc(stdin);
if (ch == '\n' || feof(stdin)) { // #3
return buf;
}
// Consume rest of line;
while (ch != '\n' && ch != EOF) { // #4
ch = fgetc(stdin);
}
if (ch == EOF) { // #5
return NULL;
}
if (reprompt) {
fputs(reprompt, stdout);
}
}
return NULL;
}
Uncommon: reading null characters remains a TBD issue.
Details for OP who is a learner.
Some tests for sane input parameters. A size of zero does not allow for any input saved as a null character terminated string. Buffers could be larger than INT_MAX, but fgets() cannot directly handle that. Code could be amended to handle 0 and huge buffers, yet leave that for another day.
fgets() does not always read a '\n'. The buffer might get full first or the last line before end-of-file might lack a '\n'. Uncommonly a null character might be read - even the first character hence the len > 0 test, rendering strlen() insufficient to determine length of characters read. Code would need significant changes to accommodate determining the size if null character input needs detailed support.
If the prior fgets() filled its buffer and the next read character attempt resulted in an end-of-file or '\n', this test is true and is OK, so return success.
If the prior fgetc() resulted in an input error, this loops exits immediately. Otherwise, we need to consume the rest of the line looking for a '\n' or EOF (which might be due to an end-of-file or input error.)
If EOF returned (due to an end-of-file or input error), no reason to continue. Return NULL.
Usage
// fgets(arr[i],25,stdin);
if (getsizedline(arr[i], sizeof(arr[i]), "Too long, try again.\n") == NULL) {
break;
}
This code uses a buffer slightly larger than the required max length. If a text line and the newline can't be read into the buffer, it reads the rest of the line and discards it. If it can, it again discards if too long (or too short).
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#define INPUTS 10
#define STRMAX 25
int main(void) {
char arr[INPUTS][STRMAX+1];
char buf[STRMAX+4];
for(int i = 0; i < INPUTS; i++) {
bool success = false;
while(!success) {
printf("Enter string %d: ", i + 1);
if(fgets(buf, sizeof buf, stdin) == NULL) {
exit(1); // or sth better
}
size_t index = strcspn(buf, "\n");
if(buf[index] == '\0') { // no newline found
// keep reading until end of line
while(fgets(buf, sizeof buf, stdin) != NULL) {
if(strchr(buf, '\n') != NULL) {
break;
}
}
if(feof(stdin)) {
exit(1); // or sth better
}
continue;
}
if(index < 1 || index > STRMAX) {
continue; // string is empty or too long
}
buf[index] = '\0'; // truncate newline
strcpy(arr[i], buf); // keep this OK string
success = true;
}
}
printf("Results:\n");
for(int i = 0; i < INPUTS; i++) {
printf("%s\n", arr[i]);
}
return 0;
}
The nice thing about fgets() is that it will place the line-terminating newline character ('\n') in the input buffer. All you have to do is look for it. If it is there, you got an entire line of input. If not, there is more to read.
The strategy then, is:
fgets( s, size_of_s, stdin );
char * p = strpbrk( s, "\r\n" );
if (p)
{
// end of line was found.
*p = '\0';
return s; (the complete line of input)
}
If p is NULL, then there is more work to do. Since you wish to simply ignore lines that are too long, that is the same as throwing away input. Do so with a simple loop:
int c;
do c = getchar(); while ((c != EOF) && (c != '\n'));
Streams are typically buffered behind the scenes, either by the C Library or by the OS (or both), but even if they aren’t this is not that much of an overhead. (Use a profiler before playing “I’m an optimizing compiler”. Don’t assume bad things about the C Library.)
Once you have tossed everything you didn’t want (to EOL), make sure your input isn’t at EOF and loop to ask the user to try again.
Putting it all together
char * prompt( const char * message, char * s, size_t n )
{
while (!feof( stdin ))
{
// Ask for input
printf( "%s", message );
fflush( stdout ); // This line _may_ be necessary.
// Attempt to get an entire line of input
if (!fgets( s, n, stdin )) break;
char * p = strpbrk( s, "\r\n" );
// Success: return that line (sans newline character(s)) to the user
if (p)
{
*p = '\0';
return s;
}
// Failure: discard the remainder of the line before trying again
int c;
do c = getchar(); while ((c != EOF) && (c != '\n'));
}
// If we get this far it is because we have
// reached EOF or some other input error occurred.
return NULL;
}
Now you can use this utility function easily enough:
char user_name[20]; // artificially small
if (!prompt( "What is your name (maximum 19 characters)? ", user_name, sizeof(user_name) ))
{
complain_and_quit();
// ...because input is dead in a way you likely cannot fix.
// Feel free to check ferror(stdin) and feof(stdin) for more info.
}
This little prompt function is just an example of the kinds of helper utility functions you can write. You can do things like have an additional prompt for when the user does not obey you:
What is your name? John Jacob Jingleheimer Schmidt
Alas, I am limited to 19 characters. Please try again:
What is your name? John Schmidt
Hello John Schmidt.
Code snippet for gets()
int main(int argc, char *argv[])
{
char str[MAX_SIZE]
gets(str);
printf("\n");
Code snippet for puts()
printf("The most probable key is: %d\n", max2);
puts(output);
return 0;
I did not paste my whole code since it seems pretty irrelevant for my question. I just want to know a way I could fix this because when I run my code through GCC, it gives me errors and is not allowing me to use gets(). How would I fix this?
Use fgets and fputs instead. There is - beside removing all the flaws of gets- also a main difference in the usage between gets and fgets: fgets stores a new line character in the buffer (and gets does not).
So an equivalent - i.e. eliminating any new line if not desired - could look as follows. Function call strcspn(buffer,"\n") gives the longest sequence of characters until a new line is encountered (or strlen(buffer), if the string does not contain a new line). By writing a 0 to the index at this position a new line - if any - is eliminated.
char buffer[MAX_SIZE] = "";
if (fgets(buffer, MAX_SIZE ,stdin)) {
buffer[strcspn(buffer,"\n")] = '\0';
}
You should absolutely, positively avoid using gets(), its dangerous and removed from the recent C standard. That's why you see the warning
C11, Foreword, Paragraph 6 mentions
Major changes from the previous edition include:
[....]
removed the gets function (<stdio.h>)
Instead, use fgets().
To add, puts() is just fine, I see no reason for replacing that one.
Never use gets(). Because it is impossible to tell without knowing the data in advance how many characters gets() will read, and because gets() will continue to store characters past the end of the buffer, it is extremely dangerous to use. It has been used to break computer security.
Use fgets() instead
char * fgets ( char * str, int num, FILE * stream );
The following example shows the usage of fgets() function.
#include <stdio.h>
int main () {
FILE *fp;
char str[60];
/* opening file for reading */
fp = fopen("file.txt" , "r");
if(fp == NULL) {
perror("Error opening file");
return(-1);
}
if( fgets (str, 60, fp)!=NULL ) {
/* writing content to stdout */
puts(str);
}
fclose(fp);
return(0);
}
alternative can I use instead of gets()
char str[MAX_SIZE]; gets() has problems when reading a line of N characters. (N also counts the '\n').
When N > MAX_SIZE, the result is undefined behavior (UB). Too much input and no place to go. Often this UB writes into places used by other objects. Bad - very bad.
C11 eliminated gets() and is not a standard function since then.
The usual fgets() solution is well suggested by #Stephan Lechner. fgets() has some short comings listed below.
str[MAX_SIZE] now needs to be str[MAX_SIZE + 1] as fgets() also saves the '\n', unlike gets(). Sometimes adding + 1 is not practical.
fgets() retains the potential '\n'. See Removing trailing newline character from fgets()
When input is excessive, fgets() simply does not read it, unlike gets(). This is well behaved (not UB) yet we are still stuck with that problem: how to detect excessive input and what to do about it?
If code can live with these, use fgets(). Otherwise, read on.
mygets() alternative
This function does not need a +1 to the size of the s buffer.
Excessively long input returns NULL. All the line is read. The s buffer is filled with the initial characters.
char *mygets(char *s, size_t n) {
char *dest = s;
// Pathological case of n==0
char dummy[1];
if (n == 0) {
n = sizeof dummy;
dest = dummy;
}
size_t i = 0;
int ch;
n--;
while ((ch = fgetc(stdin)) != '\n' && ch != EOF) {
if (i < n) {
dest[i++] = (char) ch;
} else {
s = NULL; // Not enough room
}
}
if (ch == EOF) {
if (feof(stdin)) { // end-of-file
if (i == 0) {
s = NULL;
}
} else { // input error
i = 0;
s = NULL;
}
}
dest[i] = '\0';
return s;
}
Subtle bonuses:
s buffer is well defined on rare input error. With gets/fgets buffer contents are then undefined.
Pathological size of 0 is well defined. fgets() is a bit iffy on that.
Buffer size is the idiomatic size_t rather than int as with fgets().
Usage
str[MAX_SIZE];
if (mygets(str, sizeof str)) {
printf("Success <%s>\n", str);
} else {
if (feof(str)) printf("End of file detected. <%s>\n", str);
else if (ferror(str)) printf("End of file detected. <%s>\n", str);
else printf("Input too long <%s>.", str);
}
What I'm trying to accomplish is to take no more than "x" characters (spaces included) as input. I only know how to do both of them separately with scanf,
like the following:
scanf("%20s",str)
This takes no more than 20 characters.
scanf("%[^\n]s",str) takes spaces as well, but it has no limit.
I tried getline but it takes the \n as a value in the string as well and I don't want that. I hope I was clear enough about what I'm asking.
From what #chqrlie has told me I wrote this fuction:
void getstring(char *str, int len)
{
do
{
if (fgets(str, len, stdin))
{
fflush(stdin);
// if is not the first character to be the new line then change it to '\0' which is the end of the string.
if (str[0] != '\n')
str[strcspn(str, "\n")] = '\0';
}
}while (str[0] == '\n'); // Check if the user has inserted a new line as first character
}
The format for character classes does not have a trailing s, it is written this way:
scanf("%[^\n]", str)
If you wish to limit the maximum number of characters stored into the destination array, specify this number between the % and the [:
scanf("%20[^\n]", str)
Note however that the conversion will fail and scanf() will return 0 if there is an empty line pending for this conversion specification.
It is a common mistake to omit the test on the return value of scanf(), causing undefined behavior in case of conversion failures because the destination variables are left in their previous state (uninitialized in many cases).
It may be more effective to use fgets() and remove the trailing newline this way:
if (fgets(s, 20, stdin)) {
/* line was read, can be an empty line */
s[strcspn(s, "\n")] = '\0'; /* remove the trailing newline if any */
...
} else {
/* fgets() failed, either at end-of-file or because of I/O error */
...
}
You can use the following:
for(i = 0; i < x; i++)
{
getchar(c);
if(c == '\n') break;
str[i] = c;
}
But you must have to be aware of the existing newlines in the buffer. :)
I am having the absolute craziest time getting full line input to work. I will explain my problem. I need to get a full line of input, including a space, from the user entered at the keyboard. Simple right? Wrong!
MY GOAL
Store multiple strings, with spaces, into variables. If it makes a difference, I want to make the variables equal to a char pointer. So once I get the input from tempString, I want to set it to a char pointer. Like so:
char *variable1, *variable2;
//get user input
variable1 = tempString;
//get more user input
variable 2 = tempString;
//etc etc etc
Here's what I've tried.
First try
char tempString[100];
scanf("%s", &tempString);
printf("%s", tempString);
Invalid: scanf will stop reading at a white space, so "Example String" would just end up being "Example".
Second try
So I do more research. I thought I found the magic fix.
char tempSTring[100];
fgets(tempString, 100, stdin);
printf("%s", tempString);
Originally this works. However there is a massive problem. I need to get the user to enter about 8 inputs. Meaning I have to use a command like this 8 times. The problem is the program often skips over the fgets command. If I use a scanf previously, somehow the \n character is stuck in the input stream, and automatically feeds into fgets, satisfying its stdin input, and then does not prompt the user for input.
Third try
After thinking fgets was maybe my solution with a work around, I tried some tricks.
char tempSTring[100];
getc(stdin);
fgets(tempString, 100, stdin);
printf("%s", tempString);
I tried adding this getc(stdin) line. It worked for much of my program. It absorbs the \n character left behind in the stream. When it does so, great, it works. But sometimes, for some reason, the \n is NOT left in the stream, and when debugging, it looks like getc(stdin) is requesting input from the user, so it pauses my program to ask for input.
Question
These don't work for me.
How should I be doing this easy task?
To read (up to) 8 lines from a file, you can use either of these solutions. I decline to use variables char *variable1, *variable2, …; — that is an array seeking to escape.
POSIX getline()
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
enum { MAX_LINES = 8 };
char *lines[MAX_LINES];
int index = 0;
char *buffer = 0;
size_t buflen = 0;
while (index < MAX_LINES && getline(&buffer, &buflen, stdin) != -1)
{
lines[index++] = buffer;
buffer = 0;
buflen = 0;
}
free(buffer); // Space may be allocated before EOF is detected
for (int i = 0; i < index; i++)
printf("%d: %s", i, lines[i]);
return 0;
}
If getline() fails to allocate memory, it will report an error, so there is no need to do an explicit error check.
Standard C fgets()
Code using strdup(), another POSIX function. It isn't a part of standard C (though it is widely available). It is trivial to implement.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
enum { MAX_LINES = 8 };
char *lines[MAX_LINES];
int index = 0;
char buffer[4096];
while (index < MAX_LINES && fgets(buffer, sizeof(buffer), stdin) != 0)
{
if ((lines[index] = strdup(buffer)) == 0)
break;
index++;
}
for (int i = 0; i < index; i++)
printf("%d: %s", i, lines[i]);
return 0;
}
The test in the loop allows for the possibility of strdup() failing to allocate memory.
Notes
Both the solutions above keep the newline at the end of the input string. If you don't want that, you can zap it with:
lines[i][strcspn(lines[i], "\r\n")] = '\0';
This overwrites a carriage return or newline with a null byte, transforming DOS or Unix line endings. You then need to adjust the printing which assumes the string includes a newline. Note that the expression shown works correctly even if there is no carriage return or newline in the string.
The fgets() solution will break lines at 4095 characters, leaving the rest to be read as 'the next line'. If that's not acceptable, you have a variety of strategies open to you.
You can detect whether there is a newline and arrange to allocate more memory and read the next section of the line into the extra memory, repeating until you come across a newline or EOF.
You can read the remaining characters up to the newline or EOF:
int c;
while ((c = getchar()) != EOF && c != '\n')
;
Implementing strdup()
If for some reason your system doesn't have an implementation of strdup(), you can create a surrogate with:
#include <assert.h>
#include <stdlib.h>
#include <string.h>
char *strdup(const char *old_str)
{
assert(old_str != 0);
size_t old_len = strlen(old_str) + 1;
char *new_str = malloc(old_len);
if (new_str != 0)
memmove(new_str, old_str, old_len);
return new_str;
}
Here's how we old fart C programmers would do it:
#include <stdio.h>
#define MAX_LEN 100
int main( )
{
int c;
char input[MAX_LEN+1];
int i = 0;
while ( (c=getchar()) != '\n' && c != EOF && i < MAX_LEN)
input[i++] = c;
if (c == EOF || c =='\n') {
/* received input that terminated within buffer limit */
input[i] = '\0';
printf("read in your input string of: %s\n", input);
}
else {
printf("don't buffer overflow me dude!\n");
return -1;
}
return 0;
}
But nowadays people will tell you to use one of the library functions. I'm still an old fart though.
EDIT: Fixed my embarrassing mistakes pointed out by the helpful comments below.
You can take care of '\n' left by previous scanf by writing it like this -
scanf("%d%*c", &x); //<-- example to take int input
%*c will read from stdin and then discard it, thus '\n' would be removed from stdin.
You can achieve with scanf like this (a way for your previous attempt)-
char tempString[100];
/* As suggested by chqrile it is essential to check return of scanf */
if(scanf("%99[^\n]", tempString)!=1){
// ^^ & not required
tempString[0]='\0';
}
%99[^\n] this will read 99 characters and will stop only after encountering '\n' , thus would read input with spaces.
This program essentially asks for a secret string, then asks a user to repeatedly guess single chars of that string until he guesses it all. It works however every second time the while loop is run it skips user input for the guessed char. How do I fix this?
int main(){
char guess;
char test2 [50];
char * s = test2;
char output [50];
char * t = output;
printf("Enter the secret string:\n");
fgets(test2, 50, stdin);
for (int i=0;i<49;i++){ //fills ouput with _ spaces
*(output +i)='_';
while(strcmp(s,t) != 0){
printf("Enter a guess:");
scanf("%c",&guess);
printf("You entered: %c\n", guess);
showGuess(guess,s, t ); // makes a string "output" with guesses in it
printf("%s\n",t);
}
printf("Well Done!");
}
For a quick and dirty solution try
// the space in the format string consumes optional spaces, tabs, enters
if (scanf(" %c", &guess) != 1) /* error */;
For a better solution redo your code to use fgets() and then parse the input.
As pointed out in some other answers and comments, you need to "consume" the "newline character" in the input.
The reason for that is that the input from your keyboard to the program is buffered by your shell, and so, the program won't see anything until you actually tell your shell to "pass the content of its buffer to the program". At this point, the program will be able to read the data contained in the previous buffer, e.g. your input, followed by one the character(s) used to validate your input in the shell: the newline. If you don't "consume" the newline before you do another scanf, that second scanf will read the newline character, resulting in the "skipped scanf" you've witnessed. To consume the extra character(s) from the input, the best way is to read them and discard what you read (what the code below does, notice the
while(getc(stdin) != '\n');
line after your scanf. What this line does is: "while the character read from stdin is not '\n', do nothing and loop.").
As an alternative, you could tell your shell to not buffer the input, via the termios(3) functions, or you could use either of the curses/ncurses libraries for the I/O.
So here is what you want:
int main(){
char guess;
char test2 [50];
char * s = test2; // 3. Useless
char output [50];
char * t = output; // 3. Useless
int i; // 8. i shall be declared here.
printf("Enter the secret string:\n");
fgets(test2, 50, stdin);
for (i=0;i<50;i++) if (test2[i] == '\n') test2[i] = '\0'; // 4. Remove the newline char and terminate the string where the newline char is.
for (int i=0;i<49;i++){ // 5. You should use memset here; 8. You should not declare 'i' here.
*(output +i)='_';
} // 1. Either you close the block here, or you don't open one for just one line.
output[49] = '\0'; // 6. You need to terminate your output string.
while(strcmp(s,t) != 0){ // 7. That will never work in the current state.
printf("Enter a guess:");
scanf("%c",&guess);
while(getc(stdin) != '\n');
printf("You entered: %c\n", guess);
showGuess(guess,s, t );
printf("%s\n",t);
}
printf("Well Done!");
return 0; // 2. int main requires that.
}
Other comments on your code:
You opened a block after your for loop and never closed it. That might be causing problems.
You declared your main as a function returning an integer... So you should at least return 0; at the end.
You seem to have understood that char * t = output; copies output's value and uses t as a name for the new copy. This is wrong. You are indeed copying something, but you only copy the address (a.k.a reference) of output in t. As a result, output and t refer to the same data, and if you modify output, t will get modified; and vice versa. Otherwise said, those t and s variables are useless in the current state.
You also need to remove the newline character from your input in the test2 buffer. I have added a line after the fgets for that.
Instead of setting all the bytes of an array "by hand", please consider using the memset function instead.
You need to actually terminate the output string after you "fill" it, so you should allocate a '\0' in last position.
You will never be able to compare the test2 string with the output one, since the output one is filled with underscores, when your test2 is NULL terminated after its meaningful content.
While variables at the loop scope are valid according to C99 and C11, they are not standard in ANSI C; and it is usually better to not declare any variable in a loop.
Also, "_ spaces" are called "underscores" ;)
Here is a code that does what you want:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LEN 50
int main()
{
char phrase[LEN];
char guessed[LEN];
char guess;
int i, tries = 0;
puts("Please enter the secret string:");
if(fgets(phrase, LEN, stdin) == NULL)
return 1;
for(i = 0; i < LEN && phrase[i] != '\n'; i++); // Detect the end of input data.
for(; i < LEN; i++) // For the rest of the input data,
phrase[i] = '_'; // fill with underscores (so it can be compared with 'guessed' in the while loop).
phrase[LEN - 1] = '\0'; // NULL terminate 'phrase'
memset(guessed, '_', LEN); // Fill 'guessed' with underscores.
guessed[LEN - 1] = '\0'; // NULL terminate 'guessed'
while(strcmp(phrase, guessed) != 0) // While 'phrase' and 'guessed' differ
{
puts("Enter a guess (one character only):");
if(scanf("%c", &guess) != 1)
{
puts("Error while parsing stdin.");
continue;
}
if(guess == '\n')
{
puts("Invalid input.");
continue;
}
while(getc(stdin) != '\n'); // "Eat" the extra remaining characters in the input.
printf("You entered: %c\n", guess);
for(i = 0; i < LEN; i++) // For the total size,
if(phrase[i] == guess) // if guess is found in 'phrase'
guessed[i] = guess; // set the same letters in 'guessed'
printf("Guessed so far: %s\n", guessed);
tries++;
}
printf("Well played! (%d tries)\n", tries);
return 0;
}
Feel free to ask questions in the comments, if you are not getting something. :)
Newline character entered in the previous iteration is being read by scanf. You can take in the '\n' by using the getc() as follows:
scanf("%c",&guess);
getc(stdin);
..
This changed worked for me. Though the right explanation and c leaner code is the one given by #7heo.tk
Change
scanf("%c",&guess);
with
scanf(" %c",&guess);
It should ignore '\n'.