Segmentation fault caused by fgets() in C
c, fgets, segmentation-fault
Solution
The segmentation fault is not caused by `fgets()`, but by `strcpy()`:
strcpy(*pString, buffer);
You try to write to `*pString`, but you never allocate memory for it. `pS` in `main()` is just an array of null pointers.
Another thing is with the test with `if( buffer != NULL )`, that would never be true since `buffer` is an array, not a pointer.
Problem
This is a problem I don't understand - I am using `fgets()` in main and it works. I use it (I think) in exactly the same way in a function and I get an error [Segmentation fault core dumped -- exit code 139). This code is based on a sample program in book Ivor Horton's "Beginning C" (it's a old tile but I'm just wanting to learn the basics from it). My program is as follows. I am working on *nix using Geany (basically, compiling with GCC). You can see that `fgets` works in main (output is the string you enter). But it doesn't work in the function `str_in()`. It gets as far as the second `printf()` statement to enter a string, no further. Note that in the book, Horton uses `gets()`. I am trying to implement a safer string input function here, but no joy. By the way the program is supposed to sort strings stored in an array of string pointers. ``` #include <stdio.h> #include <stdlib.h> #include <string.h> #define TRUE 1 #define FALSE 0 #define MAX_NUM_STRINGS 50 int str_in(char **); /*Pointer to a string pointer*/ void str_sort(char *[], int n); /*Array of pointers to strings, number of strings in array*/ void str_out (char *[], int n); /*Array of pointers to strings, number of strings in array*/ int main(){ char *pS[MAX_NUM_STRINGS] = { NULL }; /*Array of pointers to strings stored in str_space*/ int numStrings = 0; /*Count of strings*/ char buffer[BUFSIZ]; printf("Enter a string\n"); fgets(buffer, BUFSIZ, stdin); printf("%s", buffer); printf("fgets works here\n\n"); /* get string input from user - a pointer to each string is saved in pS */ while ( str_in(&pS[numStrings]) && numStrings < MAX_NUM_STRINGS) numStrings++; if ( numStrings > 0 ){ str_sort(pS, numStrings); str_out(pS, numStrings); } return 0; } int str_in(char** pString){ char buffer[BUFSIZ]; char *p; printf ("Enter string:\n"); fgets(buffer, 60, stdin); printf("fgets doesn't work here!!\n"); if( buffer != NULL ){ printf("here"); if ((p = strchr(buffer, '\n')) != NULL) *p = '\0'; /*replace newline with null character*/ else return FALSE; if ( strlen(buffer) > 0 ){ strcpy(*pString, buffer); return TRUE; } else return FALSE; /*blank line - end of input*/ } else return FALSE; } void str_sort(char* pStrings[], int n){ /*sort strings by manipulating array of string pointers*/ char *temp; int sorted = FALSE; int i = 0; while (!sorted){ sorted = TRUE; for(i = 0; i < n - 1; i++){ temp = pStrings[i]; if ( strcmp(temp, pStrings[i+1]) > 1 ){ pStrings[i] = pStrings[i+1]; pStrings[i+1] = temp; sorted = FALSE; break; } } } } void str_out(char* pStrings[], int n){ /*print strings to standard output. Free memory as each string is printed */ int i = 0; printf("Sorted strings:\n"); for(i = 0; i < n; i++){ printf("%s", pStrings[i]); free(pStrings[i]); } } ```