Segmentation fault (core dumped)
In C, I initialized an array of strings, like this:
char* strings[20];
then tried to fscanf a bunch of stuff.
for(int i = 0; i<20; i++){
fscanf(file, "%s", strings[i]);
}
although there is more to the program, I am sure that this is the part causing a segmentation fault. A run using gdb stated that the error was in file vfscanf, so I think this is related.
After your declaration
char* strings[20]; // This is an array of pointer of type char *
You will need to allocate memory for each pointer before you can read into them from the file.
for(int i = 0; i<20; i++){
strings[i] = malloc(some_size * sizeof(char)); // allocate memory for each pointer first.
fscanf(file, "%s", strings[i]);
}
fscanf has a problem that it does not prevent a buffer overflow if the file contained a long word; and fscanf only allows supplying a compile-time constant as the buffer length. If some_size is not a constant expression, you will need to rewrite this code to use some other input function.
char* strings[20]; does not initialize an "array of string".
Instead strings is an array of 20 char * pointers. A strings in C is array of char up to an including the trailing '\0'. So far, the array Strings[] has indeterminate values and none of the elements certainly point to a string.
By assigning those 20 pointers to various strings, you will have an "array of strings".
// Assign 0 (or NULL) to each pointer.
char* strings[20] = { 0 };
for(int i = 0; i<20; i++){
char buffer[100];
if (fscanf(file, "%99s", buffer) != 1) {
break;
}
strings[i] = strdup(buffer);
// or
size_t len = strlen(buffer) + 1;
strings[i] = memcpy(malloc(len), buffer, len); // error check omitted
}
Note that if you have a sufficiently modern POSIX-compliant version of scanf() (check your system manual), you can use:
for (int i = 0; i < 20; i++)
{
if (fscanf(file, "%ms", &strings[i]) != 1)
…report error and break/return…
}
With the %ms conversion specification, scanf() will use malloc() to allocate the appropriate amount of memory for the string it reads. Don't forget to free() the memory when you're done with it.
Note that Mac OS X (10.9.5 Mavericks) does not have a sufficiently modern version of scanf(). Linux (as found in Ubuntu 14.04, for example), does.
malloc(sizeof(char)*20)inside theforloop for each string, but it did not work. I also triedchar* strings[20] = {"","","",""...};to no avail.strings[i]=malloc(sizeof(char)*20)inside theforloop? Are you sure that all 20 strings read are no more than 19 characters (keeping in mind that you need 1 char for the null-terminating character)?