I'm getting a seg fault when after calling fgets about 20 times. I'm opening a file (does not return null). It is in the format:
num1: value1
num2: value2
num3: value3
then reading lines from the file, storing values into an array, using nums as positions. Here is the code that seg faults:
edit: declaring myArray and line:
char myArray[3000];
char * line;
char * word;
line = (char *) malloc(100);
word = (char *) malloc(16);
while(fgets(line, 99, file)) {
printf("%s\n", line);
word = strtok(line, " :");
name = (int) strtol(word, NULL, 16);
word = strtok(NULL, " \n");
myArray[name] = word;
}
you'll notice I print out the line immediately after getting it. The file has 26 lines, but it only prints 23 line and then seg faults. Now, is it something I don't fully understand about fgets, or am I getting some synthax incorrect? I've tried allocating more memory to line, or more to word. I've also tried malloc -ing more memory after every call to strtok, but nothing seems to fix the seg fault.
The problems is the line myArray[name] = word; you're taking an array index from your input line and then setting the character at that position to low bits of the address of your word... I doubt that's actually what you want to do.
There's some other problems with your code, you're leaking the memory from the line word = (char *) malloc(16); because strtok returns a pointer into the string you initially pass it. You don't actually need to malloc anything for the code as written in the question, so you could have:
char myArray[3000];
char line[100];
char *word = NULL;
word needs to be a pointer since it's holding the result of strtok()
You clearly don't understand pointers, you need to review that before you can understand why your code isn't working the way you expect.
If you say what your code is actually meant to be doing I can give you some hints on how to fix it, but at the moment I can't quite tell what the intended result is.
EDIT: Did you intend to read in your numbers in hexadecimal? The last argument to strtol() is the base to be used for conversion... you could also just use atoi()
so your loop could look like:
char myArray[3000];
char line[100];
char *word = NULL;
while(fgets(line, 100, file)) {
printf("%s\n", line);
word = strtok(line, " :");
if(word == NULL) continue;
name = atoi(word); /* only if you didn't actually want hexadecimal */
word = strtok(NULL, " \n");
if(word == NULL) continue;
if(name > 0 && name < 3000) { /* as I said in a comment below */
strncpy(myArray + name, word, 3000 - name);
}
}
Related
I need help with allocating memory to my variables. I'm looking for specific lines that are causing the crash and how to fix them. I've tried reallocating and malloc in many places and in different ways. I have a rough idea about which lines are problematic (my realoc lines?).
int main() {
char * myString;// myString uesd to hold users input as entered
myString = input1(); //Get users input and stor it in myString
int sentence_count = 0; //To keep track of the total number of lines entered
sentence * sentences; //array of sentences to hold all the sentences as an instance of sentence
sentences = NULL;//initialize all values
myprint(sentence_count, sentences, myString);//Print word and lines
search(myString, sentence_count, sentences);//Search for word in sentences
free(myString);//free the memory set aside
return 0;
}
char * input1() {
char * line;// temporary variable to one hold input line
char * myString;//myString uesd to hold users input as entered
line = (char * ) malloc(1024 * sizeof(char));
myString = malloc(1024);
myString[0] = '\0';
line[0] = '\0';
while (line[0] != '\n') {
printf(" Please input a line : ");
fgets(line, 1000, stdin);
strcat(myString, line);//add line to mystring
}
free(line);
return myString;
}
I run it on Linux on PowerShell and get the following error
Segmentation fault (core dumped)
line = (char * ) malloc(1024 * sizeof(char));
myString = malloc(1024);
while (line[0] != '\n')
It is very clear here that, you did not initialize line character array. During first iteration, line[0] is unknown. Reading uninitialized variables is undefined behavior and can result in unexpected program behavior.
I am trying to read a txt file, and I can get the line which I want, but I can not print every words in this line one by one;
for example: the line looks like:
hello world 1 2 3
and I need print them one by one which looks like:
hello
world
1
2
3
I got the segmentation fault core dumped error
char temp[256]；
while(fgets(temp, 256, fp) != NULL) {
...
int tempLength = strlen(temp);
char *tempCopy = (char*) calloc(tempLength + 1, sizeof(char));
strncpy(temCopy, temp, tempLength); // segmentation fault core dumped here；
// works fine with temp as "name country"
name = strtok_r(tempCopy, delimiter, &context);
country = strtok_r(Null, delimiter, &context);
printf("%s\n", name);
printf("%s\n", country);
}
Can anyone help me fix the code?
Thanks!
Impleted with strtok()
char *p;
char temp[256];
while(fgets(temp,256,fp) != NULL){
p = strtok (temp," ");
while (p != NULL)
{
printf ("%s\n",p);
p = strtok (NULL, " ");
}
}
If you see man strtok You will found
BUGS
Be cautious when using these functions. If you do use them, note that:
* These functions modify their first argument.
* These functions cannot be used on constant strings.
* The identity of the delimiting character is lost.
* The strtok() function uses a static buffer while parsing, so it's not thread safe. Use strtok_r() if this matters to you.
Try to make changes with strtok_r()
While read a line from a file you can invoke the following function:
if( fgets (str, 60, fp)!=NULL ) {
puts(str);
token = strtok(str," ");
while(token != NULL)
{
printf("%s\n",token);
token = strtok(NULL," ");
}
}
Hi guys I have this file struct:
0
2 4
0: 1(ab) 5(b)
1: 2(b) 6(a)
2: 0(a) 2(b)
3: 2(a) 6(b)
4: 5(ab)
5: 2(a) 6(b)
6: 4(b) 6(ab)
Each line will feed a struct with its data (numbers + letters).
What's the best way to read the line and get the strings I want?
Example:
0
2 4
0,1,ab,5,b
1,2,b,5,a
...
The lines may vary in size because we can have 1, 2, 3, .... numbers.
I already did it :
//struct
#define MAX_ 20
struct otherstats{ //struct otherStats
int conectstat[MAX_];//conection with others stats
int transitions[MAX_];//Symbols betwen conection ASCI
}tableStats[MAX_];
struct sAutomate{
int stat_initial; //initial
int stats_finals[MAX_]; //final orfinals
struct otherstats tableStats[MAX_]; //otherStats 0 1 2 3 4 5 6
};
/* eXample that what i want ..using the example
sAutomate.stat_initial=0
sAutomate.stats_finals[0]=2
sAutomate.stats_finals[1]=4
Others Stats table
//0
sAutomate.tableStats[0].conectstat[0]=1;
sAutomate.tableStats[0].conectstat[1]=5;
sAutomate.tableStats[0].transitions[0]=ab;
sAutomate.tableStats[0].transitions[1]=b;
//1
sAutomate.tableStats[1].conectstat[0]=2;
sAutomate.tableStats[1].conectstat[1]=6;
sAutomate.tableStats[1].transitions[0]=b;
sAutomate.tableStats[1].transitions[1]=a;
///etc
*/
void scanfile(){ //function to read the file
struct sAutomate st; //initialize st struct
char filename[] = "txe.txt";
FILE *file = fopen ( filename, "r" );
char buf[81];
char parts[5][11];
fscanf(file,"%d", &st.stat_initial);//read first line
printf("initial state : %d \n", st.stat_initial);
fscanf(file,"%d",&st.stats_finals);
fscanf(file,"%d",&st.stats_finals);
while (fgets(buf, sizeof(buf), stdin) != NULL)
{
if (sscanf(buf, "%10[^:]: (%10[^(], %10[^)]), (%10[^(], %10[^)])",
parts[0], parts[1], parts[2], parts[3], parts[4]) == 5)
{
printf("parts: %s, %s, %s, %s, %s\n",
parts[0], parts[1], parts[2], parts[3], parts[4]);
}
else
{
printf("Invalid input: %s", buf);
}
}
//fclose
First problem I see is you're overwriting stats_finals:
fscanf(file,"%d",&st.stats_finals);
fscanf(file,"%d",&st.stats_finals);
What you wanted to do here was:
fscanf(file,"%d",&st.stats_finals[0]);
fscanf(file,"%d",&st.stats_finals[1]);
To save off both the "2" and the "4" from the text file.
Second major problem is you're reading from stdin:
while (fgets(buf, sizeof(buf), stdin) != NULL)
That doesn't read your text file, that reads input from the keyboard... So you wanted that to be:
while (fgets(buf, sizeof(buf), file) != NULL)
Third (minor) problem is that fscanf() will not read newlines, and fgets() will. This means when you go from reading your second stats_finals to the first read in the while loop, your first input will just be the left over newline character. That's not a big deal since you check for "invalid input", but it's worth noting.
Finally, your sscanf looks wrong to me:
sscanf(buf, "%10[^:]: (%10[^(], %10[^)]), (%10[^(], %10[^)])",
^ ^
That's a width of 10, Why are you checking for commas? You didn't
I don't think that's have any in your text file
what you wanted...
I think this is more what you were looking for:
sscanf(buf, "%[0-9]: %[0-9](%[^)]) %[0-9](%[^)])",
^
takes a digit (0 to 9)
EDIT
Missed your original point. If you don't know how long the strings will be that you're reading, you can't use sscanf(). It's that simple. :)
The scanf family assumes you know how many objects you'll be parsing and the format string takes in that many. There are other options however.
Read a single line with fgets as you're doing, but then you can tokenize it. Either with the C function strtok or by your own hand with a for loop.
One note however:
Since you don't know how long it is, this: char parts[5][11]; is not your best bet. This limits you to 2 entries... probably it would be better to do this dynamically (read the line then allocate the correct size to store your tokens in.)
If you really don't know how many numbers and letters the line will contain, why are you reading a fixed amount of numbers and letters?
You could read the whole line with fgets and then parse it with a tokenizer like strtok, something like this:
const char* const DELIMITERS = " ";
int i; // index for tableStats
char* token;
token = strtok(line, DELIMITERS);
// first integer
if (token == NULL || sscanf(token, "%d:", &i) < 1)
// error
/* it seems like you should have at least one element in your "list",
* otherwise this is not necessary
*/
token = strtok(NULL, DELIMITERS);
if (token == NULL || sscanf(token, "%d(%[^)])",
&(tableStats[i].connectstat[0]),
&(tableStats[i].transitions[0])) < 2)
// error
// read optional part
for (int j = 1; (token = strtok(NULL, DELIMITERS)) != NULL; ++j)
if (sscanf(token, "%d(%[^)])", &(tableStats[i].connectstat[j]),
&(tableStats[i].transitions[j])) < 3)
break;
Remember that strtok changes the string, make a copy of it if you still need it.
Obviusly the code is for the arbitrary long lines, reading the first two lines is trivial.
I have lineget function that returns char *(it detects '\n') and NULL on EOF.
In main() I'm trying to recognize particular words from that line.
I used strtok:
int main(int argc, char **argv)
{
char *line, *ptr;
FILE *infile;
FILE *outfile;
char **helper = NULL;
int strtoks = 0;
void *temp;
infile=fopen(argv[1],"r");
outfile=fopen(argv[2],"w");
while(((line=readline(infile))!=NULL))
{
ptr = strtok(line, " ");
temp = realloc(helper, (strtoks)*sizeof(char *));
if(temp == NULL) {
printf("Bad alloc error\n");
free(helper);
return 0;
} else {
helper=temp;
}
while (ptr != NULL) {
strtoks++;
fputs(ptr, outfile);
fputc(' ', outfile);
ptr = strtok(NULL, " ");
helper[strtoks-1] = ptr;
}
/*fputs(line, outfile);*/
free(line);
}
fclose(infile);
fclose(outfile);
return 0;
}
Now I have no idea how to put every of tokenized words into an array (I created char ** helper for that purpose), so that it can be used in qsort like qsort(helper, strtoks, sizeof(char*), compare_string);.
Ad. 2 Even if it would work - I don't know how to clear that line, and proceed to sorting next one. How to do that?
I even crashed valgrind (with the code presented above) -> "valgrind: the 'impossible' happened:
Killed by fatal signal"
Where is the mistake ?
The most obvious problem (there may be others) is that you're reallocating helper to the value of strtoks at the beginning of the line, but then incrementing strtoks and adding to the array at higher values of strtoks. For instance, on the first line, strtoks is 0, so temp = realloc(helper, (strtoks)*sizeof(char *)); leaves helper as NULL, but then you try to add every word on that line to the helper array.
I'd suggest an entirely different approach which is conceptually simpler:
char buf[1000]; // or big enough to be bigger than any word you'll encounter
char ** helper;
int i, numwords;
while(!feof(infile)) { // most general way of testing if EOF is reached, since EOF
// is just a macro and may not be machine-independent.
for(i = 0; (ch = fgetc(infile)) != ' ' && ch != '\n'; i++) {
// get chars one at a time until we hit a space or a newline
buf[i] = ch; // add char to buffer
}
buf[i + 1] = '\0' // terminate with null byte
helper = realloc(++numwords * sizeof(char *)); // expand helper to fit one more word
helper[numwords - 1] = strdup(buffer) // copy current contents of buffer to the just-created element of helper
}
I haven't tested this so let me know if it's not correct or there's anything you don't understand. I've left out the opening and closing of files and the freeing at the end (remember you have to free every element of helper before you free helper itself).
As you can see in strtok's prototype:
char * strtok ( char * str, const char * delimiters );
...str is not const. What strtok actually does is replace found delimiters by null bytes (\0) into your str and return a pointer to the beginning of the token.
Per example:
char in[] = "foo bar baz";
char *toks[3];
toks[0] = strtok(in, " ");
toks[1] = strtok(NULL, " ");
toks[2] = strtok(NULL, " ");
printf("%p %s\n%p %s\n%p %s\n", toks[0], toks[0], toks[1], toks[1],
toks[2], toks[2]);
printf("%p %s\n%p %s\n%p %s\n", &in[0], &in[0], &in[4], &in[4],
&in[8], &in[8]);
Now look at the results:
0x7fffd537e870 foo
0x7fffd537e874 bar
0x7fffd537e878 baz
0x7fffd537e870 foo
0x7fffd537e874 bar
0x7fffd537e878 baz
As you can see, toks[1] and &in[4] point to the same location: the original str has been modified, and in reality all tokens in toks point to somewhere in str.
In your case your problem is that you free line:
free(line);
...invalidating all your pointers in helper. If you (or qsort) try to access helper[0] after freeing line, you end up accessing freed memory.
You should copy the tokens instead, e.g.:
ptr = strtok(NULL, " ");
helper[strtoks-1] = malloc(strlen(ptr) + 1);
strcpy(helper[strtoks-1], ptr);
Obviously, you will need to free each element of helper afterwards (in addition to helper itself).
You should be getting a 'Bad alloc' error because:
char **helper = NULL;
int strtoks = 0;
...
while ((line = readline(infile)) != NULL) /* Fewer, but sufficient, parentheses */
{
ptr = strtok(line, " ");
temp = realloc(helper, (strtoks)*sizeof(char *));
if (temp == NULL) {
printf("Bad alloc error\n");
free(helper);
return 0;
}
This is because the value of strtoks is zero, so you are asking realloc() to free the memory pointed at by helper (which was itself a null pointer). One outside chance is that your library crashes on realloc(0, 0), which it shouldn't but it is a curious edge case that might have been overlooked. The other possibility is that realloc(0, 0) returns a non-null pointer to 0 bytes of data which you are not allowed to dereference. When your code dereferences it, it crashes. Both returning NULL and returning non-NULL are allowed by the C standard; don't write code that crashes regardless of which behaviour realloc() shows. (If your implementation of realloc() does not return a non-NULL pointer for realloc(0, 0), then I'm suspicious that you aren't showing us exactly the code that managed to crash valgrind (which is a fair achievement — congratulations) because you aren't seeing the program terminate under control as it should if realloc(0, 0) returns NULL.)
You should be able to avoid that problem if you use:
temp = realloc(helper, (strtoks+1) * sizeof(char *));
Don't forget to increment strtoks itself at some point.
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 :-)