Dynamic memory and fgets?

You're not allocating space for your strings, just the array of strings. MyArrayj is just an uninitialized pointer. Instead, allocate space for each string in myArray like so.

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Hi to all stackoverflow users. I am trying to build a simple (as an exercise) code that will read from a file and will store the words from a file in an dynamically allocated array. I think I am mallocing wrong.

Does anyone see what I am doing wrong? #include #include #include #include #define ARRSIZE 10 int main(){ char * myArray = malloc(ARRSIZE*sizeof(char*)); FILE * p1File; char mystring1 100; char word 100; int j = 0; p1File = fopen ("my1file. Txt","r"); if (p1File == NULL) perror ("Error opening file"); else{ while(fgets(mystring1, 100, p1File)){ int nuRead = sscanf(mystring1, "%s", word);\ printf("lepo ani magia\n\n"); if (nuRead > 0){ strncpy (*myArrayj, mystring1, 100); //*myArrayj = mystring1; } j += 1; } } } /////////////////////////////////// my text file is this will probably work but I am c malloc pipes fgets sscanf link|improve this question asked Nov 23 '10 at 18:26Paul Kar.1479 84% accept rate.

– nmichaels Nov 23 '10 at 18:31 I get a segfault. – Paul Kar. Nov 23 '10 at 18:36.

You're not allocating space for your strings, just the array of strings. MyArrayj is just an uninitialized pointer. Instead, allocate space for each string in myArray like so: char *myArrayARRSIZE; // No reason for this to be dynamic.

// ... if (nuRead > 0) { myArrayj = malloc((strnlen(mystring, 100) + 1) * sizeof(char)); strncpy (myArrayj, mystring1, nuRead + 1); } As user411313 pointed out, sscanf doesn't return the number of characters matched, but the number of input items matched. Use strnlen (or strlen if you don't have strnlen) to get the size of the string (and don't forget to add 1 for the null terminator).

Most appreciated. :) – Paul Kar. Nov 23 '10 at 18:50 -1 big mistake.

Sscanf returns NOT the number of characters (for your malloc). Sizeof(char) is always 1. – user411313 Nov 23 '10 at 21:36 @user411313: Thanks, I'm used to a wonkified library that does return the number of characters matched.

Sizeof(char) may always be 1, but I like being explicit. It makes it obvious that I'm allocating bytes instead of words and is quicker for me to read if my malloc calls all follow the same pattern. – nmichaels Nov 23 '10 at 21:52.

For this task I would first define a data structure that holds the words, like this: struct wordlist { char **words; /* the actual words */ size_t size; /* the number of words in the list */ size_t capacity; /* the number of words that would fit in the list */ }; typedef struct wordlist wordlist; Then I would define some functions to operate on them. This is to keep the code in main short and readable. The functions are: void * malloc_or_fail(size_t size) { void *result = malloc(size); if (result == NULL) { perror("malloc"); exit(EXIT_FAILURE); } return result; } /* Creates a newly allocated copy of the given string.

Later changes * to the given string will not have any effect on the returned string. */ char * str_new(const char *str) { size_t len = strlen(str); char *result = malloc_or_fail(len + 1); memcpy(result, str, len + 1); return result; } /* Adds a copy of the given string to the word list. Later changes * to the given string have no effect on the word in the word list.

*/ void wordlist_add(wordlist *wl, const char *word) { if (wl->size == wl->capacity) { /* TODO: resize the wordlist */ } assert(wl->size capacity); wl->wordswl->size++ = str_new(word); } /* Creates a new word list that can hold 10 words before it will be * resized for the first time. */ wordlist * wordlist_new(void) { wordlist *result = malloc_or_fail(sizeof wordlist); result->size = 0; result->capacity = 10; result->words = malloc_or_fail(result->capacity * sizeof result->words0); return result; } Using these functions it shouldn't be difficult to complete the original task.

Thank you for the detailed example Roland. Most appreciated. :) – Paul Kar.

Nov 23 '10 at 22:18.

Char * myArray = malloc(ARRSIZE*sizeof(char*)); You have allocated a place to store ten string pointers. But you have not allocated any space to copy the characters into persistent strings. If you want to set up that storage at the beginning, you could do #define MAX_STR_SIZE 100 char * myArray = malloc(ARRSIZE*sizeof(char*)); if (!myArray) exit(1); for (j=0; j Instead of strncpy, use strdup (which is like doing a malloc then a strcpy): myArrayj = strdup(mystring1).

Got it. Thanks. :) – Paul Kar.

Nov 23 '10 at 18:50 1 strdup is not ANSI C – user411313 Nov 23 '10 at 21:28.

If you only need to handle up to 10 lines of text then I'd do it more like this: char *myArrayARRSIZE; ... if (nuRead > 0) { myArrayj++ = strdup(mystring1); } ... What's happening is that this code allocates and copies in one go (using strdup, rather than malloc followed by strcpy).

I see. Thank you. :) – Paul Kar.

Nov 23 '10 at 18:51.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.