How can I use fgets in VS - c

Question

I've been trying to run this code on VS2017. The code is compiling and running, but not in the way I want it too. So, I try to use the debugger and it says:
Debug Assertion Failed!
Program:
File: minkernel\crts\ucrt\src\appcrt\stdio\fgets.cpp
Line:33
Expression: stream.valid()
From past questions I understood that it may happen because of mishandling the opening of files, but I think that my code does take care of it.
Any help would be greatly appreciated!
(my relevant code):
int main(int argc, char *argv[]) {
int i, count_commands, PC_A, lastLine;
int *PC = &PC_A;
FILE *memin;
FILE *memout;
FILE *regout;
FILE *trace;
FILE *count;
assert(argc == 6);
*PC = 0;
count_commands = 0;
//allocationg memory for registers content
char **regs = (char **)(malloc(sizeof(char *) * 16));
for (i = 0; i < 16; i++) {
regs[i] = (char *)(malloc(sizeof(char) * 9));
for (int j = 0; j < 8; j++) {
regs[i][j] = '0';
}
regs[i][8] = '\0';
}
//allocationg memory for the memory image we have
char **memory = (char **)(malloc(sizeof(char *) * 4096));
for (i = 0; i < 4096; i++) {
memory[i] = (char *)(malloc(sizeof(char) * 9));
memory[i][0] = '\0';
}
//load memin image into memory
char *line = (char *)malloc(sizeof(char) * 8);
memin = fopen(argv[1], "r");
if (memin != NULL) {
perror(strerror(errno));
}
int j = 0;
while ((line = fgets(line, 10, (FILE *)memin)) != NULL) {
strcpy(memory[j], line);
memory[j][8] = '\0';
j++;
}

Answer 1

After opening the file, in OP's code there is this check:
if (memin != NULL) {
perror(strerror(errno));
}
So, if the opening succeeded an error string is printed. In my implementation, it reports:
Success: Success
No action is taken if it fails to open the file.
When it comes to the actual reading of all the lines in the file, there are some other issues. A buffer (char array) named line of size 8 is dinamically allocated and passed to fgets:
while ((line = fgets(line, 10, (FILE *)memin)) != NULL) {
// ^^
Note that 10 is also passed, as size of the buffer, which is wrong, because it allows fgets to write out of the bounds of the allocated array.
Also, given OP's compiler is MSVC 2017, I assume this code is running on Windows, so chances are that in the file, the lines are terminated by a "\r\n" sequence, rather then a single '\n'. Even if OP is confident that each line is a 8 char string, fgets needs a buffer of at least size 8 + 3 (8 + '\r' + '\n' + '\0') to read them safely.
Consider how those suggestions are implemented in this snippet:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#define MEM_SIZE 1024u
#define LINE_SIZE 128u
#define STR_SIZE 8u
int main(int argc, char *argv[])
{
// Try to open the input file
if (argc < 2) {
fprintf(stderr, "Missing file name in command line.\n");
return EXIT_FAILURE;
}
FILE *memin = fopen(argv[1], "r");
if (memin == NULL) {
fprintf(stderr, "Unable to open file [%s].\n", argv[1]);
return EXIT_FAILURE;
}
// I'd use plain arrays to store the lines
char memory[MEM_SIZE][STR_SIZE + 1] = {{'\0'}};
char line[LINE_SIZE] = {'\0'};
size_t count = 0;
while ( count < MEM_SIZE && fgets(line, LINE_SIZE, memin) ) {
size_t length = strcspn(line, "\r\n");
if (length > STR_SIZE) {
fprintf(stdout, "Warning, line too long: %zu.\n", count);
length = STR_SIZE;
}
memcpy(memory[count], line, length);
memory[count][STR_SIZE] = '\0';
++count;
}
for ( size_t i = 0; i < count; ++i ) {
printf("[%s]\n", memory[i]);
}
}