valgrind sscanf issues with arguments [closed] - c

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Im writing this program in c89 that reads the files however i keep getting segmentation fault
ive run it by valgrind --leak-check=full --show-leak-kinds=all -v ./program and it pointed to the two sscanf lines leaks
to run the program, it is two file names
./program cat.txt dog.txt
and complies by a make file
I have free'd them and set to null after and i still get these issues, i have attached a picture of my [![valgrind errors here][1]][1]
int main(int argc, char* argv[]){
char* cat = (char*)malloc(12 * sizeof (char));
char* dog = (char*)malloc(12 * sizeof (char));
/*float sleepTime;*/
/*if (argc != 4)
{
printf("Error - Enter file names");
}*/
sscanf(argv[1], "%s", cat);
sscanf(argv[2], "%s", dog);
sleepTime = atof(argv[3]);
readFile(cat);
readFile(dog);
free(cat);
free(dog);
cat = NULL;
dog = NULL;
}
i tried to comment things out, however still no luck
any help would be appreciated

Answer 1

Ok from looking at the valgrind log aswell as reading what you wrote I gather this:
You are building with a makefile, which should set the compiler arguments dog.txt and cat.txt, which are then written cat and dog.
The valgrind log says Address 0x0 is not ... in main when calling sscanf().
This means that there is a null pointer as it is pointing to an invalid memory address, being used in the sscanf() call.
So either the make build fails to properly compile with the arguments or the memory allocation of cat and dog is not successful.
.
To check validity:
I would recommend writing some assertions or writing a function to check if a pointer is vaild and call it and check your pointers, namely cat , dog and argv[index] just before calling sscanf().
https://ptolemy.berkeley.edu/~johnr/tutorials/assertions.html
https://wiki.sei.cmu.edu/confluence/display/c/MEM10-C.+Define+and+use+a+pointer+validation+function
A good and simple example of pointer validation from the above link:
int valid(void *ptr) {
return (ptr != NULL); // 1 valid, 0 invalid
}
To fix eventual makefile issues I think we would need to see the makefile in question, but if that can't be done for some reason then these might be of interest:
Command-line arguments via Makefile
How to pass argument from Makefile to a program?
Edit:
I checked the updated valgrind log on the question and noticed that the reachable memory that is in readFile().
To fix that issue you would need to define a function that properly closes the file. As you never close the files, leaving them hanging in memory causing your reachable memory warning.