I am writing a program where I use strtok in order to find each word in a string that I type into the command line, in my example, my code is called command.c so when I type:
./command.out "Hi, there"
I should get as my result:
Arg = "Hi, there"
Next word "Hi,"
Next word "there"
so far my code will complete the arg part of the print statement, but will not use execute the latter part in order to separate the string in question, my code currently is as follows:
#include <stdio.h>
#include <string.h>
void main (int argc, char *argv[]) {
int i;
for(i =1;i< argc; i++)
printf("Arg = %s\n", argv[i]);
char delims[] = " ";
char *word = NULL;
word = strtok(argv[i], delims);
while(word != NULL) {
printf("Next word \"%s\"\n", word);
word = strtok(NULL, delims);
}
}
Where am I going wrong and how can I fix this code? Thanks for all the help
You are missing the curly braces around the for block:
for(i =1;i< argc; i++)
{
printf /* ... and so forth */
}
Your code indentation is wrong, this may cause your problem.
The 'for' statement affects only the next line, the printf one, so variable 'i' increases later to value '2', then when you ask for argv[i], you're asking for argv[2], you should call argv[1].
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I'm trying to split up a string (typed in by the user at run time) into words (separated by spaces), and put each word into a different slot into an array. So, for example, if I took the string "hello world", array[0] would contain "hello" and array[1] would contain "world". And the last slot (in this case array[2]) would contain NULL. Here's what I have so far, which doesn't seem to be working properly. Any help would be appreciated. (By the way, this is part of a program which will call execvp(argv[0],argv); )
char input[100];
char* argv[20];
char* token;
scanf("%s", input);
//get the first token
token = strtok(input, " ");
int i=0;
//walk through other tokens
while( token != NULL ) {
argv[i] = token;
i++;
token = strtok(NULL, " ");
}
argv[i] = NULL; //argv ends with NULL
You need to allocate memory for each argv[i] and copy the current token to argv[i]:
token = strtok(input, " ");
int i=0;
//walk through other tokens
while( token != NULL ) {
argv[i] = malloc(strlen(token) + 1);
strncpy(argv[i], token, strlen(token));
//argv[i] = token;
i++;
token = strtok(NULL, " ");
}
argv[i] = NULL; //argv ends with NULL
I have created an example of what I think you want. I have used one malloc(3) for the whole
line of strings and another for the array of pointers you will get from the function.
Also, the second parameter of strtok(3) is passed to give more flexibility (the shell normally uses the contents of IFS environment variable to separate arguments so you can use the same algorithm as the shell does) I think you should use " \n\t" at least. It has a main() test function, so it's complete for your purpose.
#include <assert.h> /* man assert(3) */
#include <stdlib.h> /* malloc lives here */
#include <string.h> /* strtok, strdup lives here */
#include <stdio.h> /* printf lives here */
char **split(const char *str, const char *delim)
{
char *aux;
char *p;
char **res;
char *argv[200]; /* place for 200 words. */
int n = 0, i;
assert(aux = strdup(str));
for (p = strtok(aux, delim); p; p = strtok(NULL, delim))
argv[n++] = p;
argv[n++] = NULL;
/* i'll put de strdup()ed string one place past the NULL,
* so you can free(3), once finished */
argv[n++] = aux;
/* now, we need to copy the array, so we can use it outside
* this function. */
assert(res = calloc(n, sizeof (char *)));
for (i = 0; i < n; i++)
res[i] = argv[i];
return res;
} /* split */
int main()
{
char **argv =
split("Put each word of a string into array in C", " ");
int i;
for (i = 0; argv[i]; i++)
printf("[%s]", argv[i]);
puts(""); /* to end with a newline */
free(argv[i+1]);
free(argv);
} /* main */
The sample code just outputs:
$ pru
[Put][each][word][of][a][string][into][array][in][C]
I think I just figured out my problem: I need to use gets() instead of scanf(), because scanf() only gets the first word, up until a space, while I want to be able to get a string containing multiple words separated by spaces.
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.
I have a string that contains with spaces, such as "print 2" or "print 3 test". I'm trying to remove the first argument - in these examples, the print.
I tried strtok():
char *test;
test = strtok(COMMAND, " ");
printf("%s\n", test);
However printing test will segfault. I tried making a function, and it works fine from main() but when called from the function I need it in, it also segfaults.
char* split(char S[], int N) {
printf("Running split() on %s\n", S);
int Spaces = 1;
int i = 0;
for (i; i<strlen(S) && Spaces <=N; i++) {
if (S[i] == ' ') {
Spaces++;
}
}
printf("split: %s\n", &S[i]);
//return "0";
return &S[i];
}
I'm guessing it's some kind of pointer problem. Command is being passed into the print function like so:
Print(File, Lines, COMMAND);
I don't know what COMMAND is in your test sample, but you should test, if strtok returns null (when strtok can't find a token).
printf with a nullpointer will give you a seg vault.
Normally you call strtok from a loop:
http://www.cplusplus.com/reference/clibrary/cstring/strtok/
always test the return value of strtok()!
If no such byte (2nd parameter) is found, ie. no tokens exist in the string pointed to by the 1st parameter, a null pointer is returned.
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 :-)
Reads through a .txt file and puts all chars that pass isalpha() in a char array. for spaces it puts \0, so the characters in the array are separated by strings. This works.
I need help with the second part. I need to read a string that the user inputs (lets call it the target string), find all instances of the target string in the char array, and then for each instance:
1. print the 5 words before the target string
2. print the target string itself
3. and print the 5 words after the target string
I can't figure it out, i'm new to C in general, and I find this i/o really difficult after coming from Java. Any help would be appreciated, here's the code I have right now:
#include <stdio.h>
#include <string.h>
main(argc, argv)
int argc;
char *argv[];
{
FILE *inFile;
char ch, ch1;
int i, j;
int arrayPointer = 0;
char wordArray [150000];
for (i = 0; i < 150000; i++)
wordArray [i] = ' ';
/* Reading .txt, strip punctuation, conver to lowercase, add char to array */
void extern exit(int);
if(argc > 2) {
fprintf(stderr, "Usage: fread <filename>\n");
exit(-1);
}
inFile = fopen(argv[1], "r");
ch = fgetc(inFile);
while (ch != EOF) {
if(isalpha(ch)) {
wordArray [arrayPointer] = tolower(ch);
arrayPointer++;
}
else if (isalpha(ch1)) {
wordArray [arrayPointer] = '\0';
arrayPointer++;
}
ch1 = ch;
ch = fgetc(inFile);
}
fclose;
/* Getting the target word from the user */
char str [20];
do {
printf("Enter a word, or type \"zzz\" to quit: ");
scanf ("%s", str);
char* pch;
pch = strstr(wordArray, str);
printf("Found at %d\n", pch - wordArray + 1);
pch = strstr(pch + 1, str);
} while (pch != NULL);
}
There are a number of problems here, but the one that is probably tripping you up the most is the use of strstr as you've got it. Both parameters are strings; the first is the haystack, and the second is the needle. The definition of a C string is (basically) a sequence of characters terminated by '\0'. Take a look at how you've constructed your wordArray; it's effectively a series of strings one right after the other. So when you are using strstr the first time, you are only ever looking at the first string.
I realize this isn't the entire answer you are looking for, but hopefully it points you in the right direction. You may want to consider building up an array of char * that points into your wordArray at each word. Iterate over that new array checking for the string the user is looking for. If you find it, you now have an index you can work backwards and forwards from.