What I am trying to do is to break the user input in parts with whitespace as a delimiter, copy the parts into the array (tokenAr) and compare the tokenAr[0] (the first part) if it is equal to sHistory. if they are equal, check the value of tokenAr[1] if it is "1", "2" etc, to execute the corresponding command that is entered in the history array. This is what i have tried to far and it crashes. I am using TCC on Windows x64.
EDIT: I forgot to mention that I began learning C, just two days ago.
EDIT2: I run the program in a debugger and it has raised an Acces Violation(Segmentation Fault) in line if(strcmp(tokenArPtr[0],sHistory)==0)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[])
{
int i=1; int j=1; int k=0;
char history[100][100] = {0};
char sKey[] = "exit";
char sInput[100];
char sHistory[]="history";
do
{
//gather user input
printf ("hshell> ");
fgets (sInput, 100, stdin);
strcpy(history[i],sInput);
i++;
//END_gather user input
//Tokenizing
char delims[] = " ";
char *tokenArPtr[5];
char *result = NULL;
result = strtok(sInput, delims);
tokenArPtr[0] = result;
while (result!=NULL)
{
puts(result);
result= strtok(NULL, delims);
tokenArPtr[k+1] = result;
puts(tokenArPtr[k]);
puts("=====");
k++;
}
k=0;
/*
//END_Tokenizing
if(strcmp(tokenArPtr[0],sHistory)==0)
{
for(j=1;j<i;j++)
{
printf("%d. %s \n",j,history[j]);
}
}
else if (strcmp (sKey,tokenArPtr[0]) != 0)
{
printf("\nCommand not found \n");
}*/
}while (strcmp (sKey,sInput) != 0);
return 0;
}
EDIT 3: I used the result variable instead of the tokenArPtr directly, but when debugging, I noticed that the values of the array are not being updated.
Which type does strtok return? char *. What is the type of tokenAr[k]? char. What type does strcmp expect as input? char * and char *. What is the type of tokenAr[0]? char.
See a problem? You should. The * is pretty significant.
Assuming tokenAr is declared like char *tokenAr[2];, how many char * values can tokenAr store? What happens when k exceeds 2? You need to ensure you don't overflow your tokenAr array.
history is uninitialised. Using an uninitialised variable is undefined behaviour. I suggest initialising it, like this: char history[100][100] = { 0 };
Which book are you reading?
While tokenizing, the loop will never end because the test is on the variable "result" that will never change... So you're finally going to a buffer overflow with "tokenAr"... Modify your code to test "tokenAr".
Edit: And tokenAR should be an array... (I don't know how it can compile...)
There are many problems... First of all you should include string.h which will show you some errors in compilation.
I believe that the main problem is here:
char tokenAr[2];
result = strtok(sInput, delims);
while (result!=NULL)
{
tokenAr[k] = strtok(NULL, delims);
k++;
}
tokenAr should be an array of pointers, not chars. And are you sure that k will never exceed 2? An assertion would help debugging.
Related
I am trying to make a program that will encrypt and decrypt when user enters the string they want to encrypt/decrypt for argv[2] and enters either "encrypt" or "decrypt" for argv[3]. Here is the code I am trying to compile and run as of now
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv)
{
int i;
// char *string;
char *key_ch;
char key_int;
char *string_ = calloc(80, 1);
string = argv[1];
char encrypted_string[strlen(string)];
char decrypted_string[strlen(string)];
//char *key_ch;
//char key_int;
string = argv[1];
key_ch = argv[2];
key_int = atoi(key_ch);
if (argc < 3)
{
printf("Not enough arguments!\n");
exit (1);
}
if (strcmp(argv[3], "encrypt") == 0)
{
i = 0;
while(i <= strlen(string)-1)
{
encrypted_string[i] = string[i] + key_int;
i++;
}
// printf("Encrypted string: ");
i = 0;
while (i <= strlen(string) -1)
{
printf("%c", encrypted_string[i]);
i++;
}
printf("\n");
}
if (strcmp(argv[3], "decrypt") == 0)
{
i = 0;
while(i <= strlen(string) -1)
{
decrypted_string[i] = string[i] - key_int;
i++;
}
// printf("Decrypted String: ");
i = 0;
while (i <= strlen(string) -1)
{
printf("%c", decrypted_string[i]);
i++;
}
printf("\n");
}
return 0;
}
When I try to compile it without the -Wall command it compiles fine but when I run the program I am getting a segmentation fault, when I compile with -Wall I am getting
sam0.c:9:24: warning: 'string' is used uninitialized in this function [-Wuninitialized]
char encrypted_string[strlen(string)];
Can anyone possible shine some light on this error? Thank you
Edit:
Changed my code to your suggestions. I am not getting a compiling error at all even when using "-Wall" however somewhere in my program it is causing me to get a segmentation fault... any ideas? I put quotes around where I changed my code for reference in case I did it wrong.
warning: 'string' is used uninitialized in this function
[-Wuninitialized]
char *string; creates a pointer to char. At this point it is not yet a string, but you are using it as a string argument.
Before using char *string; it must have memory assigned, and should be initialized. Among other methoods, this can be done by:
char *string = calloc(80, 1);//initializes with known values (NULL).
Now string is usable, but has zero length. Values can be assigned via string functions:
strcpy(string, argv[1]);
sprintf(string, "%s", argv[1]);
strcat(string, argv[1]);
... more string functions
When using input from command line, argv, argc, malloc/calloc and string cpy functions can be avoided by using strdup. a value can be assigned like this:
if(argc == 2)
{
char *string = strdup(argv[1]);
if(!string) return -1;
...
EDIT (addressing your OP edit)
You are now using two different variables: string_ and string
char *string_ = calloc(80, 1);
^
string = argv[1];
Make them the same throughout your code and it should build and run.
When a meaningful value for the variable can be determined, try to declare and initialize the variable in one step:
char *string = argv[1];
char encrypted_string[strlen(string)];
char decrypted_string[strlen(string)];
char *key_ch = argv[2];
char key_int = atoi(key_ch);
This will fix the warning: you were trying to get the length of an uninitialized string.
(here assuming C99. char encrypted_string[strlen(string)] is a VLA. If you're restricted to C89 only Rykker's answer works).
Also:
use const to prevent unwanted modifications, e.g.
const char *string = argv[1];
/* ... */
const char *key_ch = argv[2]
string is a constant so you can get its length just one time (do not recalculate the length every time... take a look at Shlemiel the painter's algorithm). So
const char *string = argv[1];
const int length = strlen(string);
char encrypted_string[length];
char decrypted_string[length];
const char *key_ch = argv[2];
char key_int = atoi(key_ch);
check inputs: what happen if
argc < 4
argv[3] isn't in ("encrypt", "decrypt")
key_ch is not a number
key_int is too big
you're printing encrypted_string / decryped_string one character at a time... and it works, but consider that if you want to manipulate them as 'strings' they aren't null terminated and their length isn't correct.
don't repeat yourself. The differences between the encryption and the decryption phases are minimal: you can use just one buffer and change key_int to a negative value to decrypt.
char *string;
char encrypted_string[strlen(string)];
char decrypted_string[strlen(string)];
This results in undefined behavior - you try to get the length of an uninitialized piece of memory (I'm amazed that your program doesn't crash). You may only call strlen after assigning something to string.
The easiest fix (assuming you don't want to start using malloc, strdup, etc.) would be moving the last two lines after string = argv[1];
Also, you need to check argc to make sure enough arguments have been passed!
Ok, so I'm going to explain my program.
It takes a text file that's setup as such: in pairs, first line being the title of an experiment, and the second line being 10 numbers separated by spaces. It saves the first lines of pairs in *experiments and the second lines of pairs in data. The last line is *** END *** which is what it's supposed to end with.
For some reason *** END *** doesn't end the program. Any ways I can fix this? I'm assuming it's because fgets gives str blank spaces (99 chars total) so that the string in quotes will never be equal to str?
Thanks.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
int var;
int i=0,j,k;
char seps[] = " ";
char *experiments[20];
int data[10][20];
char str[100]; // make sure that this size is enough to hold the single line
char *ptr, *token;
int no_line=1;
while(fgets(str,100,stdin) != NULL && strcmp(str,"*** END ***"))
{
if(no_line % 2 == 0)
{
k=0;
token = strtok (str, seps);
while (token != NULL)
{
sscanf (token, "%d", &var);
data[i][k++] = var;
token = strtok (NULL, seps);
}
i++;
/*read integer values from the string "str" using sscanf, sscanf can be called in a loop with %d untill it fails */
}
else
{
ptr = strdup(str);
experiments[i] = ptr;
/*strore string in your variable "experiments" , before copying allocate a memory for the each entry */
}
no_line++;
}
for(j=0;j<i;j++)
{
printf("%s",experiments[j]);
for(k=0;k<10;k++)
{
printf("%d ",data[j][k]);
}
printf("\n");
}
}
You're declaring i here ...
int i,j,k;
... and using it here ...
data[i][k++] = var;
Nowhere do you initialize i. Also, why does data need to be a 2D array? Can't it just be a 1D array?
int data[10];
...
data[k++] = var;
From this code, int i seems to be declared, but not initialized?
data[i][k++] = var;
It may be helpful to use Eclipse or Code Block IDE to try small testable codes because it has all sorts of syntax and error checking features.
I already asked on question earlier about the string function strstr, and it just turned out that I had made a stupid mistake. Now again i'm getting unexpected results and can't understand why this is. The code i've written is just a simple test code so that I can understand it better, which takes a text file with a list of 11 words and i'm trying to find where the first word is found within the rest of the words. All i've done is move the text document words into a 2D array of strings, and picked a few out that I know should return a correct value but are instead returning NULL. The first use of strstr returns the correct value but the last 3, which I know include the word chant inside of them, return NULL. If again this is just a stupid mistake I have made I apologize, but any help here on understanding this string function would be great.
The text file goes is formatted like this:
chant
enchant
enchanted
hello
enchanter
enchanting
house
enchantment
enchantress
truck
enchants
And the Code i've written is:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[]) {
FILE* file1;
char **array;
int i;
char string[12];
char *ptr;
array=(char **)malloc(11*sizeof(char*));
for (i=0;i<11;i++) {
array[i]=(char *)malloc(12*sizeof(char));
}
file1=fopen(argv[1],"r");
for (i=0;i<11;i++) {
fgets(string,12,file1);
strcpy(array[i],string);
}
ptr=strstr(array[1],array[0]);
printf("\nThe two strings chant and %s yield %s",array[1],ptr);
ptr=strstr(array[2],array[0]);
printf("\nThe two strings chant and %s yield %s",array[2],ptr);
ptr=strstr(array[4],array[0]);
printf("\nThe two strings chant and %s yield %s",array[4],ptr);
ptr=strstr(array[5],array[0]);
printf("\nThe two strings chant and %s yields %s",array[5],ptr);
return 0;
}
Get rid of the trailing \n after fgets().
for (i=0;i<11;i++) {
fgets(string, sizeof string, file1);
size_t len = strlen(string);
if (len > 0 && string[len-1] == '\n') string[--len] = '\0';
strcpy(array[i], string);
}
char *chomp(char *str){
char *p = strchr(str, '\n');
if(p)
*p = '\0';
return str;
}
...
strcpy(array[i], chomp(string));
Here's the code, which is supposed to execute the first command in history when "history 1" is entered:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main (int argc, char *argv[])
{
int i=0; int j=0; int k=0;
char inputString[100];
char *result=NULL;
char delims[] = " ";
char historyArray[100][100] = {0};
char *tokenArray[100][100] ;
do
{
j = 0;
printf("hshell>");
gets(inputString);
strcpy (historyArray[k], inputString);
k++;
// Break the string into parts
result = strtok(inputString, delims);
while (result!=NULL)
{
//result2 = result;
strcpy(tokenArray[j], result);
//puts(result);
j++;
result= strtok(NULL, delims);
//puts(tokenArray[j]);
}
//j = 0;
puts(tokenArray[0]);
puts(tokenArray[1]);
if (strcmp(tokenArray[0], "exit") == 0)
{
return 0;
}
else if (strcmp(tokenArray[0], "history") == 0)
{
if (j>1)
{
strcpy (result,historyArray[atoi(tokenArray[j-1])]);
}
else
{
//print history array
for (i=0; i<k;i++)
printf("%i. %s\n", i+1, historyArray[i]);
}
}
else
{
printf("Command not found\n");
}
}while (1);
}
However, it crashes. When in debugging, I noticed two things: - the array (tokenArray) address is out of bounds and - Access Violation (Segmentation Fault). You can see the errors in the images below.
What am I missing? What am I doing wrong?
The reason why you are dealing with segmentation fault is because you are trying to copy a string into the memory that has not yet been allocated. You have defined result as a char* and just assigned NULL to it, so trying to copy string into it is wrong:
char *result = NULL;
// ...
strcpy(result, historyArray[atoi(tokenArray[j-1])]);
You need to allocate some memory, that result will point to. Then strcpy can be used to copy string into this memory. You can either use malloc to allocate it dynamically or you can define result as an temporary variable with automatic storage duration (i.e. char result[100];).
Also note that
char *tokenArray[100][100];
defines a two-dimensional array of pointers to char. But what you actually need in this case is an array of strings, so you need to get rid of * just like #cnicutar has pointed out.
And one more note:
strcpy(result,historyArray[atoi(tokenArray[j-1])]);
is quite dangerous thing to do, because when atoi fails, you are trying to access the element out of array bounds, which produces undefined behavior, thus I recommend you doing something like this:
char tokenArray[100][100] = {0};
int index;
char indexString[100] = "8";
if (sscanf(indexString, "%d", &index) == 1) // integer successfully retrieved
{
strcpy(tokenArray[index], "some string");
printf("%s", tokenArray[8]);
}
You probably meant char tokenArray[100][100]; which creates 100 tokens with 100 characters each in 1 token.
writing char *tokenArray[100][100] literally means tokenArray is an array of 100 arrays, which contain 100 char *. But each of those char * points to a random addresses if it is not assigned a proper address.
You are getting a segmentation violation error because one of the char * contains an address which you cannot access.
Well, I declared a global array of chars like this char * strarr[];
in a method I am tokenising a line and try to put everything into that array like this
*line = strtok(s, " ");
while (line != NULL) {
*line = strtok(NULL, " ");
}
seems like this is not working.. How can I fix it?
Thanks
Any number of things could be going wrong with the code you haven't shown us, such as undefined behaviour by strtoking a string constatnt, or getting your parameters wrong when calling the function.
But the most likely problem from the code we can see is the use of *line instead of line, assuming that line is of type char *.
Use the following code as a baseline:
#include <stdio.h>
#include <string.h>
int main (void) {
char str[] = "My name is paxdiablo";
// Start tokenising words.
char *line = strtok (str, " ");
while (line != NULL) {
// Print current token and get next word.
printf ("[%s]\n", line);
line = strtok(NULL, " ");
}
return 0;
}
This outputs:
[My]
[name]
[is]
[paxdiablo]
and should be easily modifiable into something you can use.
Be aware that, if you're trying to save the character pointers returned from strtok (which would make sense for using *line), they are transitory and will not be what you expect after you're done. That's because modifications are made in-place within the source string. You can do it with something like:
#include <stdio.h>
#include <string.h>
int main (void) {
char *word[4]; // The array of words.
size_t i; // General counter.
size_t nextword = 0; // For preventing array overflow.
char str[] = "My name is paxdiablo";
// Start tokenising.
char *line = strtok (str, " ");
while (line != NULL) {
// If array not full, duplicate string to array and advance index.
if (nextword < sizeof(word) / sizeof(*word))
word[nextword++] = strdup (line);
// Get next word.
line = strtok(NULL, " ");
}
// Print out all stored words.
for (i = 0; i < nextword; i++)
printf ("[%s]\n", word[i]);
return 0;
}
Note the specific size of the word array in that code above. The use of char * strarr[] in your code, along with the message tentative array definition assumed to have one element is almost certainly where the problem lies.
If your implementation doesn't come with a strdup, you can get a reasonably-priced one here :-)