I was reading BeeJ's C programming guide and copied his readline() function, that reads a line from stdin. Due to the way it's implemented it has no problem reading multibyte characters, as it reallocates the spaces in accordance with the total amount of received bytes, and as such, it has no problem with unicode input. Here's a program with the function included:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define printPrompt printf("db > ")
/* The readLine function, allocates memory for a short string and
** reads characters into it. When the string's size limit is met,
** the same memory block is reallocated, but twice the size.
** Shamelessly stolen from BeeJ's guide to C programming |=
*/
char* read_line(void) {
int i = 0; /* Position of the current character */
int linbuf = 4; /* Size of our line in memory, will be
duplicated once the line length surpasses it */
char* lin; /* The pointer value to our line */
int c; /* The value we'll use to accept characters */
if( !(lin = malloc( linbuf*sizeof(char))) )
return NULL;
while( c = getchar(), c != '\n' && c != EOF ) {
/* Check if the amount of bytes accepted has surpassed the
* amount of memory we've allocated so far */
if(i == linbuf - 1) {
/* If it did, reallocate double the space */
linbuf *= 2;
char* tmpbuf = realloc(lin, linbuf);
/* If the space couldn't have been allocated then we'd
* run out of memory. Delete everything and abort. */
if(tmpbuf == NULL) {
free(tmpbuf);
return NULL;
}
/* If we've arrived here that means there were no
* problems, so we'll assign the newly reallocated
* memory to "lin" */
lin = tmpbuf;
}
/* Add the new character to our allocated space */
lin[i++] = c;
}
/* If we've received an EOF signal after having read 0
* characters, we'd like to delete our allocated memory and
* return a NULL */
if(c == EOF && i == 0) {
free(lin);
return NULL;
}
/* Here we'll shrink the allocated memory to perfectly fit our
* string */
if(i < linbuf - 1) {
char* tmpbuf = realloc(lin, i + 1);
if(tmpbuf != NULL)
lin = tmpbuf;
}
/* Here we'll terminate the string */
lin[i] = '\0';
/* Finally, we'll return it */
return lin;
}
int main(int argc, char* argv[]) {
char* hey = read_line();
printf("%s\n", hey);
return 0;
}
An input of
Hello, World! (:
would result in the output of
Hello, World! (:
An input of multibyte characters such as
שלום, עולם! (:
would result in the correct output of
שלום, עולם! (:
However, if I were to press the backspace key, it would only delete a one byte character, resulting in garbled output; an input of (backspaces marked as \b):
שיהיה לכם בוקר טוב\b\b\b\b\b\b\b\bערב טוב
which is supposed to end up being:
שיהיה לכם ערב טוב
actually ends up being:
�שיהיה לכם בוק�ערב טוב
My computer runs a Musl-libc version of Void Linux, and I compiled the program with both tcc and gcc, both yielding the same results.
Does this problem have to do with my libc, with my terminal (suckless st), with my kernel, or is it something I'm missing in the code? Whatever might be the case, is there any way I can handle it, preferably without using any external libraries such as ICU or what have you?
"is there any way I can handle it [...] without using any external libraries" The answer is a big fat no. Unless you are prepared to write a big and complex library yourself, that is.
With external libraries this is trivial:
sudo apt install libreadline-dev # no idea how to say that in Void
#include <stdio.h>
#include <readline/readline.h>
#include <readline/history.h> // optional, to enable line history
int main()
{
using_history(); // optional
char* s;
while ((s = readline("Type something > ")))
{
printf("You have typed: %s\n", s);
add_history(s);
}
printf ("Bye!\n");
}
With this, you get a bunch of goodies for free, including full Unicode-aware line editing, programmable keybindings, and input history.
Edit On a machine I first checked this, your program behaved like you describe. But on another machine, which happens to be my home desktop, it works as expected, no weird backspace behaviour at all. I checked both X11 terminals and the text linux tty. So I guess there is something with some kernels and/or terminals after all.
Later edit There is an stty setting that controls this behaviour, at least for UTF-8.
stty iutf8
and your program should behave as expected, with no big fat libraries needed.
Related
I'm working with Code::Blocks and the thing is I tried many times to fix the problem with the Conio library and probably some other libraries as well. Every time I use something like clrscr(); textcolor(); or anything it says ;
Undefined reference to textcolor.
For example, this simple program is supposed to show the sum in a specific color but it's not working out though I have seen it work before.
#include <stdio.h>
#include <conio.h>
int fx(int x,int y,int z)
{
return x+y+z;
}
int main()
{
int a,b,c;
printf("Enter three values to a, b and c.\n");
scanf("%d%d%d",&a,&b,&c);
int total=fx(a,b,c);
textcolor(14);
printf("Output ="); cprintf(" %d",&total);
getch();
return 0;
}
P.S.: I'm using GNU GCC. And sometimes when I select another compiler or just open Code::Blocks it says, "Some plugins are missing," or something like that.
Can anyone help??
conio.h is not supported with gcc.
conio.h is not supported by gcc. Here is an implementation of conio.h for gcc though.
conio.h is not supported in gcc. You may try the curses library, which supports creation of text-user interface.
There are many flavor of curses, you may use ncurses or pdcurses library with code-blocks.
Some of the functions in the original Borland conio.h are easy to duplicate -- I've recently been porting from Turbo-C programs (from 1990!) to gcc, and found versions of getch and getche (for Linux) that I could use online (but not the C++ version, which won't compile using the gcc command). I wrote my own version of cgets, but haven't found the need to create my own versions of the other functions from that header file yet.
char getch()
{
char c; // This function should return the keystroke without allowing it to echo on screen
system("stty raw"); // Raw input - wait for only a single keystroke
system("stty -echo"); // Echo off
c = getchar();
system("stty cooked"); // Cooked input - reset
system("stty echo"); // Echo on - Reset
return c;
}
char getche()
{
char c; // This function should return the keystroke, with echo to screen
system ("stty raw"); // Raw input - wait for only a single keystroke
c = getchar();
system ("stty cooked"); // Cooked input - reset
return c;
}
char *cgets(char *buf)
/* gets a string from console and stores it in *buf; buf[0] must be initialized to maximum string size and *buf must
be declared by caller to maximum string size plus 3 bytes, to accommodate string, terminating null, size byte in buf[0]
and length of entered string in buf[1]; sets buf[1] to length of string entered and returns pointer to buf[2] */
{
/* declare and initialize internal variables */
unsigned int count = 2; /* start at 2 because [0] is max size including terminator and [1] returns actual */
/* entry size, also including terminating null */
char input = '\0'; /* initialize to null */
/* start actual function */
while (count < buf[0] + 2) /* while within permitted string length -- +2 for size control bytes */
{
input=getch(); /* get a single character, without echo */
if (input != (char) 13) /* not cr/enter key -- presumed meaningful input */
{
printf("%c",input);
buf[count++] = input; /* store character and increment counter */
}
else
{
buf[count] = '\0'; /* change cr/enter key to terminating null */
buf[1]=(char) count - 2;/* store length of entered string (including terminating null) */
count = buf[0] + 2; /* terminate entry loop -- +2 for size control again */
}
}
return &buf[2]; /* return pointer to start of string */
}
The key thing to remember is that an included file (such as conio.h) doesn't have to be precompiled; it can be just as functional if it's just more C source code.
Try this library: https://sourceforge.net/projects/coniohcloneturboccpp/.
The CONIO features for Windows and Linux are almost complete. It seems to work well.
For a class, I've been given the task of writing radix sort in parallel using pthreads, openmp, and MPI. My language of choice in this case is C -- I don't know C++ too well.
Anyways, the way I'm going about reading a text file is causing a segmentation fault at around 500MB file size. The files are line separated 32 bit numbers:
12351
1235234
12
53421
1234
I know C, but I don't know it well; I use things I know, and in this case the things I know are terribly inefficient. My code for reading the text file is as follows:
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
int main(int argc, char **argv){
if(argc != 4) {
printf("rs_pthreads requires three arguments to run\n");
return -1;
}
char *fileName=argv[1];
uint32_t radixBits=atoi(argv[2]);
uint32_t numThreads=atoi(argv[3]);
if(radixBits > 32){
printf("radixBitx cannot be greater than 32\n");
return -1;
}
FILE *fileForReading = fopen( fileName, "r" );
if(fileForReading == NULL){
perror("Failed to open the file\n");
return -1;
}
char* charBuff = malloc(1024);
if(charBuff == NULL){
perror("Error with malloc for charBuff");
return -1;
}
uint32_t numNumbers = 0;
while(fgetc(fileForReading) != EOF){
numNumbers++;
fgets(charBuff, 1024, fileForReading);
}
uint32_t numbersToSort[numNumbers];
rewind(fileForReading);
int location;
for(location = 0; location < numNumbers; location++){
fgets(charBuff, 1024, fileForReading);
numbersToSort[location] = atoi(charBuff);
}
At a file of 50 million numbers (~500MB), I'm getting a segmentation fault at rewind of all places. My knowledge of how file streams work is almost non-existent. My guess is it's trying to malloc without enough memory or something, but I don't know.
So, I've got a two parter here: How is rewind segmentation faulting? Am I just doing a poor job before rewind and not checking some system call I should be?
And, what is a more efficient way to read in an arbitrary amount of numbers from a text file?
Any help is appreciated.
I think the most likely cause here is (ironically enough) a stack overflow. Your numbersToSort array is allocated on the stack, and the stack has a fixed size (varies by compiler and operating system, but 1 MB is a typical number). You should dynamically allocate numbersToSort on the heap (which has much more available space) using malloc():
uint32_t *numbersToSort = malloc(sizeof(uint32_t) * numNumbers);
Don't forget to deallocate it later:
free(numbersToSort);
I would also point out that your first-pass loop, which is intended to count the number of lines, will fail if there are any blank lines. This is because on a blank line, the first character is '\n', and fgetc() will consume it; the next call to fgets() will then be reading the following line, and you'll have skipped the blank one in your count.
The problem is in this line
uint32_t numbersToSort[numNumbers];
You are attempting to allocate a huge array in stack, your stack size is in few KBytes (Moreover older C standards don't allow this). So you can try this
uint32_t *numbersToSort; /* Declare it with other declarations */
/* Remove uint32_t numbersToSort[numNumbers]; */
/* Add the code below */
numbersToSort = malloc(sizeof(uint32_t) * numNumbers);
if (!numbersToSort) {
/* No memory; do cleanup and bail out */
return 1;
}
I have been trying to program a UNIX style shell command prompt in C. Within this program I need it to keep track of the commands that have already been used, so the user can recall the last command by entering 'r'. I made a globally initialized array to hold strings. Whenever the array of characters a user entered needs to be saved, I add it to the global array. I have tried memcpy, simply copying each value using a loop, and just copying the pointer. None of these have been working. I am not super familiar with C and I am sure it is a pointer problem.
Whenever I copy the pointer of inputBuffer to my global array string (it does get copied), however upon leaving the setup function this pointer disappears? I am not exactly sure what I am doing wrong.
Test:
(1)user input --> ls
string[0] = ls
(2)user input --> r
inputBuffer = ls
string[recent] = ls
incorrectly does...
inputBuffer = r
string[recent] = r
(I have included the relevant parts of the code.)
#define MAX_LINE 80 /* 80 chars per line, per command, should be enough. */
#define SAVED_BUFFER 100
char *string[SAVED_BUFFER];
int p = 0;
int recent = -1;
int stringSize = 0;
void setup(char inputBuffer[], char *args[],int *background)
{
int length, /* # of characters in the command line *
/* read what the user enters on the command line */
length = read(STDIN_FILENO, inputBuffer, MAX_LINE);
start = -1;
if (length == 0)
exit(0); /* ^d was entered, end of user command stream */
if (length < 0){
perror("error reading the command");
exit(-1); /* terminate with error code of -1 */
}
if (inputBuffer[0] == 'r' && inputBuffer[1] == '\n' && stringSize > 0) {
int k;
memcpy(inputBuffer, string[recent], strlen(string[recent]) + 1);
printf("%s",inputBuffer);
printf("%s",string[recent]);
}
else {
string[p] = inputBuffer;
printf("%s", string[0]);
stringSize++;
recent++; // one behind strings current array location, to get history
p++; // current string array spot
}
}
int main(void)
{
char inputBuffer[MAX_LINE]; /* buffer to hold the command entered */
int background; /* equals 1 if a command is followed by '&' */
char *args[MAX_LINE/2+1];/* command line (of 80) has max of 40 arguments */
while (1) { /* Program terminates normally inside setup */
background = 0;
printf("COMMAND2->");
fflush(0);
setup(inputBuffer, args, &background); /* get next command */
}
}
When you "save the input buffer" you actually only store a pointer to the inputBuffer array:
string[p] = inputBuffer;
The actual data is not copied, you just store a pointer to the global input buffer. When the next input replaces the old content of inputBuffer, you will see the new content even if you access it through string[recent].
The calls to memcpy don't actually do anything, since the passed input and output buffer all refer to the same memory.
To actually store a copy of the data you have to allocate new memory to store the copy. Since you are dealing with strings, this is most easily done with strdup(), which duplicates a string:
string[p] = strdup(inputBuffer);
Later, once you are done with such a copy and don't need it anymore you have to free the memory used by the copy:
free(string[p]);
Have you tried changing
char *string[SAVED_BUFFER];
to
char string[SAVED_BUFFER][MAX_LINE];
I think that's how you're treating it in the code
I'm working on a small C program for a college assignment and I've noticed a weird bug in my code. I use an iMac with the short keyboard generally, but its battery was flat so i plugged in a standard USB keyboard with number pad.
The weird thing is that if I hit [Enter] on my number pad, it seems to do what the regular [Enter} key does, but the \n I am trying to detect in the stdin function I made to read the keyboard input, doesn't work when I use the number pad's [Enter] key.
Wtf?
Here is my function that reads the user input:
/* This is my implementation of a stdin "scanner" function which reads
* on a per character basis until the the termination signals are found
* and indescriminately discarding all characters in the input in excess
* of the supplied (limit) parameter. Eliminates the problem of 'left-over'
* characters 'polluting' future stdin reads.
*/
int readStdin(int limit, char *buffer)
{
char c;
int i = 0;
int read = FALSE;
while ((c = myfgetc(stdin)) != '\n' && c != '\0') {
/* if the input string buffer has already reached it maximum
limit, then abandon any other excess characters. */
if (i <= limit) {
*(buffer + i) = c;
i++;
read = TRUE;
}
}
/* clear the remaining elements of the input buffer with a null character. */
for (i = i; i < strlen(buffer); i++) {
*(buffer + i) = '\0';
}
return read;
}
/* This function used to wrap the standard fgetc so that I can inject programmable
* values into the stream to test my readStdin functions.
*/
int myfgetc (FILE *fin) {
if (fakeStdIn == NULL || *fakeStdIn == '\0')
return fgetc (fin);
return *fakeStdIn++;
}
NB: The myfgetc and the subsequent *fakeStdIn are part of a way that I can unit test my code and 'inject' items into the stdin stream programatically as someone suggested on this question: How do I write a testing function for another function that uses stdin input?.
What output do you get for this tiny test?
#include <stdio.h>
int main(int argc, char* argv[]) {
int c;
while((c=getchar()) != EOF) {
printf("%d\n", c);
}
return 0;
}
Could well be that on Mac, you are getting \r\n, not just \n.
So it turns out that it's a Mac OSX thing. I've spoken to other Mac users and they have the same problem. Never found a fix because one may simply not exist. The problem doesn't occur on Solaris machines and since that's the OS which the code will be run on, I guess it doesn't really matter.
I am going to answer this myself with the answer that its just one of those OSX "quirks" and be done with it.
I'm working on a class project in which I must write a command line shell with the following requirements:
The shell must able to read buffered input
Buffer should be 64 characters
Error conditions should be handled
Exceeded buffer size
Interruptions (when a signal arrives) – see the man page for read()
Invalid input (unparsable characters, blank lines, etc)
Any other error that may be encountered.
Shell must have a history of at least 20 items, and the history must not be of a static size. When the history buffer is full, the oldest item is removed and the newest item added.
Programs should be able to run in the foreground or background. (using &)
Ctrl-D will exit the shell
Ctrl-C will print the complete history
The Command ‘history’ will also print the complete history. Newest items will be at the bottom of the list.
All other signals will be trapped and displayed to the user in the shell
Program will use the read() command to read in input, unless the arrow keys are supported
I have opted to implement arrow keys for history cycling, so I'm using ncurses for input, rather than read(). I think I'm doing all right using strtok() to parse input, and fork() and execvp() to run the processes, but I'm not doing all right implementing ncurses correctly. All I've gotten it to do so far is init a new screen, display the prompt, then segfault upon any key press. Not good.
I reckon the problem must be in my design. I'm not wrapping my head around ncurses too well. What sort of data structures should I be using for this project? How should I handle the ncurses setup, teardown, and everything in between? What's the deal with windows and screens, and should I have a single globally accessible window/screen that I work with? Also, I've been trying to use a char* for the input buffer, and a char** for the command history, but I have no experience in C, so despite reading up on malloc, calloc, and realloc, I'm not sure of the best way to store commands in the buffer and the history. Any tips on managing these char arrays?
tl;dr: How do I use ncurses correctly to make a command line shell, and how do I handle the command memory management with C?
I realize this is a pretty hefty question. :(
edit: I have already seen http://www.gnu.org/software/libc/manual/html_node/Implementing-a-Shell.html and http://www.linuxinfor.com/english/NCURSES-Programming/ but the ncurses documentation has actually too much overhead. I just want to use its ability to recognize arrow keys.
Here's some sample code which:
Performs dynamic memory allocation.
Reads from the console in non-blocking mode.
Uses VT100 codes to print a frame buffer to the console.
It compiles on Linux using GCC without warnings or errors. It's far from bug free, but it should give you some ideas of what's possible. Compile and run it, pressing [up] and [down] will print messages, typing characters and hitting [enter] will "execute" the command.
#include <poll.h>
#include <signal.h>
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
/** VT100 command to clear the screen. Use puts(VT100_CLEAR_SCREEN) to clear
* the screen. */
#define VT100_CLEAR_SCREEN "\033[2J"
/** VT100 command to reset the cursor to the top left hand corner of the
* screen. */
#define VT100_CURSOR_TO_ORIGIN "\033[H"
struct frame_s
{
int x;
int y;
char *data;
};
static int draw_frame(struct frame_s *frame)
{
int row;
char *data;
int attrib;
puts(VT100_CLEAR_SCREEN);
puts(VT100_CURSOR_TO_ORIGIN);
for (row = 0, data = frame->data; row < frame->y; row++, data += frame->x)
{
/* 0 for normal, 1 for bold, 7 for reverse. */
attrib = 0;
/* The VT100 commands to move the cursor, set the attribute, and the
* actual frame line. */
fprintf(stdout, "\033[%d;%dH\033[0m\033[%dm%.*s", row + 1, 0, attrib, frame->x, data);
fflush(stdout);
}
return (0);
}
int main(void)
{
const struct timespec timeout = { .tv_sec = 1, .tv_nsec = 0 };
struct frame_s frame;
struct termios tty_old;
struct termios tty_new;
unsigned char line[128];
unsigned int count = 0;
int ret;
struct pollfd fds[1];
sigset_t sigmask;
struct tm *tp;
time_t current_time;
/* Set up a little frame. */
frame.x = 80;
frame.y = 5;
frame.data = malloc(frame.x * frame.y);
if (frame.data == NULL)
{
fprintf(stderr, "No memory\n");
exit (1);
}
memset(frame.data, ' ', frame.x * frame.y);
/* Get the terminal state. */
tcgetattr(STDIN_FILENO, &tty_old);
tty_new = tty_old;
/* Turn off "cooked" mode (line buffering) and set minimum characters
* to zero (i.e. non-blocking). */
tty_new.c_lflag &= ~ICANON;
tty_new.c_cc[VMIN] = 0;
/* Set the terminal attributes. */
tcsetattr(STDIN_FILENO, TCSANOW, &tty_new);
/* Un-mask all signals while in ppoll() so any signal will cause
* ppoll() to return prematurely. */
sigemptyset(&sigmask);
fds[0].events = POLLIN;
fds[0].fd = STDIN_FILENO;
/* Loop forever waiting for key presses. Update the output on every key
* press and every 1.0s (when ppoll() times out). */
do
{
fds[0].revents = 0;
ret = ppoll(fds, sizeof(fds) / sizeof(struct pollfd), &timeout, &sigmask);
if (fds[0].revents & POLLIN)
{
ret = read(STDIN_FILENO, &line[count], sizeof(line) - count);
if (ret > 0)
{
line[count + ret] = '\0';
if (strcmp(&line[count], "\033[A") == 0)
{
snprintf(frame.data, frame.x, "up");
count = 0;
}
else if (strcmp(&line[count], "\033[B") == 0)
{
snprintf(frame.data, frame.x, "down");
count = 0;
}
else if (line[count] == 127) // backspace
{
if (count != 0) { count -= ret;}
}
else if (line[count] == '\n')
{
snprintf(frame.data, frame.x, "entered: %s", line);
count = 0;
}
else
{
count += ret;
}
}
}
/* Print the current time to the output buffer. */
current_time = time(NULL);
tp = localtime(¤t_time);
strftime(&frame.data[1 * frame.x], frame.x, "%Y/%m/%d %H:%M:%S", tp);
/* Print the command line. */
line[count] = '\0';
snprintf(&frame.data[(frame.y - 1) * frame.x], frame.x, "$ %s", line);
draw_frame(&frame);
}
while (1);
/* Restore terminal and free resources. */
tcsetattr(STDIN_FILENO, TCSANOW, &tty_old);
free(frame.data);
return (0);
}
If your input buffer is defined to be 64 characters, then I would recommend using a char array instead of a char*. Something like char input_buffer[65]; should serve your purposes (add an extra character for the trailing '\0').
As far as command history goes, you can use a two-dimensional array for that. Something like char command_history[20][65]; should let you store 20 old commands of 64 characters each.
Allocating these buffers statically should make things a bit easier for you, as you won't have to worry about malloc and friends.
It's hard to give you too much specific advice without seeing your code. I have a feeling that you are making the same type of mistakes that are typical to people first learning C. Can you post the part of your code that is giving you problems so that we can learn more about what you are doing?
Update after posted provided code:
One problem I'm seeing is that the function takeInput doesn't have a return statement. When you use input = takeInput(); inside your main function, the value of input isn't being set to what you think it is. It's probably not a valid pointer, which is causing your line that says input[j] to segfault.
Your usage of cmdHistory also needs revisiting. You allocate it with cmdHistory = (char**)calloc(21,sizeof(int));, which gives you enough space to store 21 integers. In the function printHistory, you pass elements of cmdHistory to printw as if they were strings (they're only integers). This is most definitely not doing what you want it to do. Instead, your allocation logic for cmdHistory needs to look more like your de-allocation logic (except backwards). Allocate an array of char**, then iterate through the array, assigning each pointer to a newly-allocated buffer. Just like you have one free statement for each element in the array plus a free for the array as a whole, you should have one malloc for each element plus one malloc for the array as a whole.
Even if you can't use a statically-allocated stack, try writing your program using one anyway. This will let you work the kinks out of your key detection logic, etc without having to worry about the dynamic memory part of the program. Once the rest of it is working, go back in and swap out the static memory for dynamic memory allocation. That way, you're only having to debug a little bit at a time.
Have you looked at the Readline library? It's ideal for use in your project.
http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html