I was trying to split the array I received as an argument in a function using strtok() and it simply don't work as expected.
For example I receive this string : "ls -l" and I got only "ls".
Furthermore , I want to store the tokens into an array of strings.
Here is what I have done so far:
int mysystem(char *s) {
int i;
char *tok , *aux;
int conta = 0;
int pid, status;
int j = 0;
tok = strtok(s , " ");
while (tok != NULL) {
tok = strtok(NULL, s);
conta++;
}
char *store[conta];
i = 0;
aux = strtok(s ," ");
while (aux != NULL) {
store[i] = aux;
aux = strtok(NULL, s);
i++;
}
pid = fork();
if (pid == 0)
execvp(store[0], store);
while (j != conta) {
wait (&status);
j++;
}
return 0;
}
This is the main of where I'm passing the string to my function :
int main(int args, char **arg) {
int i;
int s;
int f = 0;
if (args >= 2) {
int length = 0;
for (i = 1; i < args; ++i) {
length += strlen(arg[i]);
}
char *output = (char*)malloc(length + 1);
char *dest = output;
i = 1;
while (i < args) {
dest = strcat (dest,arg[i]);
i++;
if (i < args) {
dest = strcat (dest," ");
}
}
dest = strcat(dest, "\0");
s = mysystem(dest);
free(output);
return s;
}
}
strtok modifies the string, so you can't run it twice on the same string. s has been converted to a series of strings separated by NUL characters. Change to using an array which is "long enough" and just go through s once.
Related
I am trying to write my own Shell in C. I have a problem. I wrote my own _strtok function that uses strtok but returns all the tokens as an array of strings. For testing I use the string "ls -laR" defined in the main function. I get the valgrind error "Invalid write of size 8" when trying to malloc the number of chars in the second pointer in the array of strings named "Doubl". Why is it doing this? I am allocating the proper number of pointers to strings in the doubl array. Any insight or help would be appreciated
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
char **_strtok(char *str, char *delim)
{
char **doubl;
char *s = str;
char *string;
int i = 0;
while (*s)
{
if (*s == *delim)
i++;
s++;
}
doubl = malloc(sizeof(char *) * i + 1);
i = 0;
string = strtok(str, delim);
while (1)
{
doubl[i] = malloc(sizeof(char) * strlen(string) + 1);
strcpy(doubl[i], string);
i++;
if (string == NULL)
break;
string = strtok(NULL, delim);
}
return (doubl);
}
char *get_path(char **env)
{
char **check = env;
char *path = NULL;
char pth[] = "PATH";
int i, j, stop = 0;
for (i = 0; check[i] && stop == 0; i++)
{
for (j = 0; j < 4 && stop == 0; j++)
{
if (check[i][j] != pth[j])
break;
if (check[i][j] == pth[j] && j == 3)
{
path = malloc(strlen(check[i]));
strcpy(path, check[i]);
stop = 1;
}
}
}
return (path);
}
char **cmd_to_arg(char **cmd, char **env)
{
/* FREE PATH BEFORE END */
char *path = get_path(env);
char *slash = "/";
char **args = NULL, **check = _strtok(path, ":"), **checkStart = check, **cmdStart = cmd;
int status = -1, i = 0, j;
while (*checkStart)
{
strcat(*checkStart, slash);
strcat(*checkStart, cmd[0]);
status = access(*checkStart, F_OK | X_OK);
printf("%s\n", *checkStart);
if (status == 0)
break;
checkStart++;
}
for(;*cmdStart; i++, cmdStart++)
printf("%d\n", i);
args = malloc(sizeof(char *) * i);
args[0] = malloc(strlen(*checkStart));
strcpy(args[0], *checkStart);
puts(args[0]);
for (j = 1; j < i && cmd[j] != NULL; j++)
{
//printf("%d\n", j);
args[j] = malloc(strlen(cmd[j]) * sizeof(char));
strcpy(args[j], cmd[j]);
puts(args[j]);
}
return (args);
}
int main(int ac, char **av, char **env)
{
(void)ac, (void)av, (void)env;
char line[] = "ls laR";
//size_t size = 0;
char **cmd; //**cmdStart;
//int i = 0, j = 0;
cmd = _strtok(line, " ");
cmd = cmd_to_arg(cmd, env);
return (0);
}
I have a variable length string that I am trying to divide from plus signs and study on:
char string[] = "var1+vari2+varia3";
for (int i = 0; i != sizeof(string); i++) {
memcpy(buf, string[0], 4);
buf[9] = '\0';
}
since variables are different in size I am trying to write something that is going to take string into loop and extract (divide) variables. Any suggestions ? I am expecting result such as:
var1
vari2
varia3
You can use strtok() to break the string by delimiter
char string[]="var1+vari2+varia3";
const char delim[] = "+";
char *token;
/* get the first token */
token = strtok(string, delim);
/* walk through other tokens */
while( token != NULL ) {
printf( " %s\n", token );
token = strtok(NULL, delim);
}
More info about the strtok() here: https://man7.org/linux/man-pages/man3/strtok.3.html
It seems to me that you don't just want to want to print the individual strings but want to save the individual strings in some buffer.
Since you can't know the number of strings nor the length of the individual string, you should allocate memory dynamic, i.e. use functions like realloc, calloc and malloc.
It can be implemented in several ways. Below is one example. To keep the example simple, it's not performance optimized in anyway.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
char** split_string(const char* string, const char* token, int* num)
{
assert(string != NULL);
assert(token != NULL);
assert(num != NULL);
assert(strlen(token) != 0);
char** data = NULL;
int num_strings = 0;
while(*string)
{
// Allocate memory for one more string pointer
char** ptemp = realloc(data, (num_strings + 1) * sizeof *data);
if (ptemp == NULL) exit(1);
data = ptemp;
// Look for token
char* tmp = strstr(string, token);
if (tmp == NULL)
{
// Last string
// Allocate memory for one more string and copy it
int len = strlen(string);
data[num_strings] = calloc(len + 1, 1);
if (data[num_strings] == NULL) exit(1);
memcpy(data[num_strings], string, len);
++num_strings;
break;
}
// Allocate memory for one more string and copy it
int len = tmp - string;
data[num_strings] = calloc(len + 1, 1);
if (data[num_strings] == NULL) exit(1);
memcpy(data[num_strings], string, len);
// Prepare to search for next string
++num_strings;
string = tmp + strlen(token);
}
*num = num_strings;
return data;
}
int main()
{
char string[]="var1+vari2+varia3";
// Split the string into dynamic allocated memory
int num_strings;
char** data = split_string(string, "+", &num_strings);
// Now data can be used as an array-of-strings
// Example: Print the strings
printf("Found %d strings:\n", num_strings);
for(int i = 0; i < num_strings; ++i) printf("%s\n", data[i]);
// Free the memory
for(int i = 0; i < num_strings; ++i) free(data[i]);
free(data);
}
Output
Found 3 strings:
var1
vari2
varia3
You can use a simple loop scanning the string for + signs:
char string[] = "var1+vari2+varia3";
char buf[sizeof(string)];
int start = 0;
for (int i = 0;;) {
if (string[i] == '+' || string[i] == '\0') {
memcpy(buf, string + start, i - start);
buf[i - start] = '\0';
// buf contains the substring, use it as a C string
printf("%s\n", buf);
if (string[i] == '\0')
break;
start = ++i;
} else {
i++;
}
}
Your code does not have any sense.
I wrote such a function for you. Analyse it as sometimes is good to have some code as a base
char *substr(const char *str, char *buff, const size_t start, const size_t len)
{
size_t srcLen;
char *result = buff;
if(str && buff)
{
if(*str)
{
srcLen = strlen(str);
if(srcLen < start + len)
{
if(start < srcLen) strcpy(buff, str + start);
else buff[0] = 0;
}
else
{
memcpy(buff, str + start, len);
buff[len] = 0;
}
}
else
{
buff[0] = 0;
}
}
return result;
}
https://godbolt.org/z/GjMEqx
Let's assume I have a char buffer with data separated with char ":";
char pt[256] = "pt:ct:mac";
char *plain_text;
char *cipher_text;
char *mac;
char *next = NULL;
char *tokens = NULL;
const char sep[2] = ":";
tokens = strtok_r(pt, sep, &next);
do
{
if(i == 0)
{
int ln = strlen(tokens);
plain_text = (char*)malloc(ln * 1);
i++;
continue;
}
if(i == 1)
{
int ln = strlen(tokens);
cipher_text = (char*)malloc(ln * 1);
i++;
continue;
}
if(i == 2)
{
int ln = strlen(tokens);
mac = (char*)malloc(ln * 1);
i++;
continue;
}
}
while((tokens = strtok_r(NULL, sep, &next)) != NULL);
free(plain_text);
free(cipher_text);
free(mac);
, so the question is how in the right way to deal with strtok_r output results.
Basically, the main aim is to get the results out of pt string, and put it in the dynamic containers. Since, I don't know the size of plain_text and cipher_text.
Is it the right way to program it?
Apart from that, if do see some minor mistakes or something can be written with better practices please do let me know ;) Thank you!
I would do it with array of pointers.
char pt[256] = "pt:ct:mac";
char *next = NULL;
char *token = NULL;
char *tokens[3] = {NULL};
const char sep[2] = ":";
token = strtok_r(pt, sep, &next);
while(token)
{
int ln = strlen(token);
tokens[i]= (char*)malloc((ln * sizeof(char)) + 1);
strcpy(tokens[i],token);
i++;
token = strtok_r(NULL, sep, &next);
}
for (int i = 0; i< 3 && tokens[i]; i++) {
free(tokens[i]);
tokens[i] = NULL;
}
I am writing a microshell program as homework at my university.
Everything goes well besides one function that's not doing exactly what I'd wish it did.
I am quite new to C programming, always used higher level languages.
In fact the only times I worked with C was fiddling around with Arduino.
So I've got a line of what user inputs on the prompt. I'm trying to split it into an array of strings separated by space.
I initialized an array with
char **args = NULL;
args = malloc(sizeof(char *) * LINE_LENGTH);
And I'm sending it to a function parse_line(line, args)
The function looks like this:
bool parse_line(char *line, char **arr) {
size_t i = 0;
char *point;
point = strtok(line, " ");
while (point != NULL) {
arr[i] = malloc(strlen(point) + 1);
strcpy(arr[i], point);
point = strtok(NULL, " ");
i++;
}
arr[i] = NULL;
if (!arr)
return false;
return true;
}
The thing is that afterwards in the arr resides only first token from the splitted up line.
I am debugging it and though variable 'point' gets the right values, they aren't copied into my array. Why? I don't know.
Oh.. and the line is an array of chars, dynamic one.
char * line = NULL;
line = read_input_line();
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/wait.h>
#define LINE_LENGTH 50
void clear_screen();
void display_prompt(bool clearscr);
char * read_input_line();
void print_line(char *line);
bool parse_line(char *line, char **arr);
int main() {
bool initialRun = true;
while (true) {
// display prompt on the screen
display_prompt(initialRun);
if (initialRun)
initialRun = false;
// read input line from terminal
char * line = NULL;
line = read_input_line();
// basic commands
if (line == NULL)
continue;
if (strcmp(line, "exit") == 0) {
free(line);
exit(EXIT_SUCCESS);
} else if (strcmp(line, "clear") == 0) {
clear_screen();
continue;
}
// parse line into array
char **args = NULL;
args = malloc(sizeof(char *) * LINE_LENGTH);
if (!parse_line(line, args)) {
printf("Error during parsing command \n");
continue;
}
}
return 0;
}
void clear_screen() {
printf("\e[2J\e[H");
}
void display_prompt(bool clearscr) {
if (clearscr)
clear_screen();
printf(" > ");
}
char * read_input_line() {
char * line = (char *)malloc(sizeof(char) * LINE_LENGTH);
if (!fgets(line, LINE_LENGTH, stdin))
return NULL;
size_t len = strlen(line);
if (len > 0 && line[len-1] == '\n') {
line[--len] = '\0';
}
return line;
}
void print_line(char *line) {
printf("%s \n", line);
}
bool parse_line(char *line, char **arr) {
size_t i = 0;
char *point;
point = strtok(line, " ");
while (point != NULL) {
arr[i] = (char *)malloc(strlen(point) + 1);
strcpy(arr[i], point);
point = strtok(NULL, " ");
i++;
}
arr[i] = NULL;
for (int j=0; j<i; j++) {
printf("%s\n", arr[i]);
}
if (!arr)
return false;
return true;
}
Input:
ls -l -h
arr[i] = NULL;
for (int j=0; j<i; j++) {
printf("%s\n", arr[i]);
}
You are not using j as index so you send NULL to printf(). It's undefined behavior.
I propose you an example of implementation(still not the best but for a beginner that enough):
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define LINE_LENGTH 50
char **parse_line(char *line, size_t *n);
int main(void) {
while (true) {
// display prompt on the screen
printf(" > ");
// read input line from terminal
char line[LINE_LENGTH];
if (!fgets(line, sizeof line, stdin)) {
return 1;
}
line[strcspn(line, "\n")] = '\0';
if (strcmp(line, "exit") == 0) {
exit(EXIT_SUCCESS);
} else if (strcmp(line, "clear") == 0) {
printf("\e[2J\e[H");
continue;
}
// parse line into array
size_t n;
char **args = parse_line(line, &n);
if (!args) {
printf("Error during parsing command \n");
continue;
}
for (size_t i = 0; i < n; i++) {
printf("%s\n", args[i]);
}
}
}
char **parse_line(char *line, size_t *n) {
char **arr = malloc(sizeof *arr);
size_t i = 0;
for (char *token = strtok(line, " "); token != NULL; token = strtok(NULL, " ")) {
char **tmp = realloc(arr, sizeof *tmp * (i + 2));
if (tmp == NULL) {
for (size_t j = 0; j < i; j++) {
free(arr[j]);
}
free(arr);
return NULL;
}
arr = tmp;
arr[i] = malloc(strlen(token) + 1);
if (arr[i] == NULL) {
for (size_t j = 0; j < i; j++) {
free(arr[j]);
}
free(arr);
return NULL;
}
strcpy(arr[i], token);
i++;
}
arr[i] = NULL;
*n = i;
return arr;
}
while(token != NULL)
{
// for(position = strcspn(str,token); position >= 0;
// position = strcspn(str, token + 1));
// {
// str2[position] = count++;
// }
}
I think I'm having a logic issue with my code. I'm trying to take in a string from user input and return how many times each word was used and only return each word one time. I think my issue is within the section I have commented out but I'm not entirely sure how to fix or change my code.
For example:
Input: Hello, my cat is saying Hello.
Output: Hello 2
my 1
cat 1
is 1
saying 1
I have modified your code and written little differently,
Please have a look.
int main()
{
char haystack[50] = "Hello my cat is saying Hello";
char needle[10];
int i = 0,j = 0,k = 0;
char *ret = NULL;
int cnt = 0;
while(haystack[i] != NULL)
{
if(haystack[i] == ' ')
{
i++;
}
else
{
//Get each sub strings.
while((haystack[i] != ' ') && (haystack[i] != NULL))
{
needle[k++] = haystack[i];
i++;
}
needle[k] = '\0';
printf("The substring is: %s", needle);
//Find how many times the sub string is there in the string
while(strstr(haystack, needle) != NULL)
{
ret = strstr(haystack, needle);
//Once the Substring is found replace all charecter of that substring with space.
for(j=0;j<k;j++)
{
*(ret+j) = ' ';
}
cnt++;//Count the no of times the substrings found.
}
printf("= %d\n",cnt);
cnt = 0;
k = 0;
}
}
return(0);
}
I have not taken care for the special characters, You can modify to take care of those.
So I have used the string "Hello my cat is saying Hello" instead of "Hello, my cat is saying Hello.". Removed the Comma.
Hope this Helps.
To compute how many times a word is present in a string or line you need a structure to preserve all the different words you have and mainly how many times each word is frequent.
My simple approach, without any optimization, is:
#include <stdio.h>
#include <stdlib.h>
struct wordsDetail
{
char word[100];
int freq;
} wordsDetail;
void updateWords(struct wordsDetail s[], int length, char *token)
{
int i;
for (i = 0; i < length && s[i].word[0] != '\0'; i++) {
if (strcmp(s[i].word, token) == 0) {
s[i].freq++;
return;
}
}
strcpy(s[i].word, token);
s[i].freq++;
}
void printResults(struct wordsDetail s[], int length) {
printf("Words\tFreq\n");
for (int i = 0; i <length && s[i].word[0] != NULL; i++) {
printf("%s\t%d\n", s[i].word, s[i].freq);
}
}
int main(void)
{
struct wordsDetail myWords[100];
int wordsDetailLength = sizeof(myWords) / sizeof(wordsDetail);
const size_t line_size = 1024;
char *str = NULL;
int *str2 = NULL;
int i = 0;
char *token;
for (i = 0; i < wordsDetailLength; i++) {
myWords[i].word[0] = '\0';
myWords[i].freq = 0;
}
if ((str = calloc(line_size, sizeof(char))) == NULL) {
printf("error\n");
exit(-1);
}
printf("Input: ");
if (scanf("%[^\n]", str) != 1) {
printf("error\n");
exit(-1);
}
printf("Output: \n");
token = strtok(str, " .,!");
while (token != NULL) {
updateWords(myWords, wordsDetailLength, token);
token = strtok(NULL, " .,!");
}
printResults(myWords, wordsDetailLength);
return 0;
}
A simple result is:
Input: Hello, my cat is saying Hello to my cat.
Output:
Words Freq
Hello 2
my 2
cat 2
is 1
saying 1
to 1