How to get back pointer of pointers from a function - c

Question

I have a function which open a file, read its content line by line and then push it to an array. I have managed to get the array functionnal inside the right function, but when I want to get it back to my main function, I cannot get any items of my array.
Some code will help you to understand:
My main function:
/* ----------------- MAIN ------------ */
int main(int argc, char *argv[]) {
/*... some useless code for now ... */
char **ptrLines = NULL;
ptrLines = readEventFile(ptrParam, ptrLines);
outputExecTrace(WAR, "PTRLINES x : %x", ptrLines);
outputExecTrace(WAR, "PTRLINES char[] : %s", *(ptrLines + 2));
return EXIT_SUCCESS;
}
My fileReader function:
char** readEventFile(Parameters *parameters, char **arrLine) {
FILE *fp = fopen(parameters->inputFilePath, "r");
if (fp == NULL)
exit(0);
char line[128];
int nbCharOfLine = 0;
while(1) {
fgets(line, sizeof(line), fp);
if (feof(fp))
break;
nbCharOfLine++;
}
fclose(fp);
arrLine = malloc(sizeof(line) * nbCharOfLine);
nbCharOfLine = 0;
fp = fopen(parameters->inputFilePath, "r");
while(1) {
fgets(line, sizeof(line), fp);
if (line[0] != '#') {
arrLine[nbCharOfLine] = malloc((strlen(line)+1) * sizeof(char));
strcpy(arrLine[nbCharOfLine], line);
nbCharOfLine++;
}
if (feof(fp))
break;
}
fclose(fp);
outputExecTrace(WAR, "ARRLINE x : %x", arrLine);
outputExecTrace(WAR, "ARRLINE char[] : %s", *(arrLine + 2));
return arrLine;
}
Has it is, my outputs are the followings:
WARNING: ARRLINE int : -2020552688
WARNING: ARRLINE char[] : 1 3 4 //This is the result I am looking for.
WARNING: PTRLINES int : -2020552688 // Same as ARRLINE
Segmentation fault (core dumped) // And this is because ptrLines[2] doesn't contains anything... but why ?!
How can I fix this ?

Answer 1

It's hard to tell exactly what happen, because you have several small problems within code, which could lead to this, try to change your code in following way:
char** readEventFile(char* fileName) {
char line[128];
int nbCharOfLine = 0;
FILE *fp = fopen(fileName, "r");
if (fp == NULL)
exit(1);
while (!feof(fp)) {
char *r = fgets(line, sizeof(line), fp); // NOTE: proper handling of fgets return value
if ((r != NULL) && (line[0] != '#'))
nbCharOfLine++;
}
fclose(fp);
char **arrLine = calloc(nbCharOfLine, sizeof(char*)); // use calloc to be sure
nbCharOfLine = 0;
fp = fopen(fileName, "r");
while (!feof(fp)) {
char *r = fgets(line, sizeof(line), fp);
if ((r != NULL) && (line[0] != '#')) {
arrLine[nbCharOfLine] = calloc(strlen(line) + 1, sizeof(char));
strcpy(arrLine[nbCharOfLine++], line);
}
}
fclose(fp);
return arrLine;
}
in your main, you will call this function like:
char **ptrLines = readEventFile(ptrParam->inputFilePath);

Answer 2

Not so sure this is the whole problem, but the posted code:
while(1) {
fgets(line, sizeof(line), fp);
if (line[0] != '#') {
arrLine[nbCharOfLine] = malloc((strlen(line)+1) * sizeof(char));
strcpy(arrLine[nbCharOfLine], line);
nbCharOfLine++;
}
if (feof(fp))
break;
}
is not the right approach for several reasons,
including that function feof()
is only asserted 'true' when the code has tried to read past the
end of the file.
suggest:
while( fgets(line, sizeof(line), fp) )
{
if (line[0] != '#')
{
if( NULL == (arrLine[nbCharOfLine] = malloc((strlen(line)+1) * sizeof(char)) ) )
{ // then, malloc failed
perror( "malloc failed" );
// close file and free all malloc'd areas
exit( EXIT_FAILURE );
}
// implied else, malloc successful
strcpy(arrLine[nbCharOfLine], line);
nbCharOfLine++;
}
}