fgets is returning a blank screen - c

Question

I am new to C, this is my first project and have been teaching myself. Within my program, one of my functions needs to read a line from a file, and store it in a char array. When I trace the program with gdb the array (line[]) is simply zeros. This leads to my program returning the error "Error: a line in the asset file lacks a ':' separator\n"
Here is my code:
//return the line number (0 based) that the cmd is on, -1 if absent
int locateCmd(char cmd[]) {
int lineIndex = -1; //-1, because lineIndex is incramented before the posible return
char cmdTemp[10] = "\0";
//create a compareable cmd with correct cmd that has its remaining values zeroed out
char cmdCmp[10] = "\0";
memset(cmdCmp, 0, sizeof(cmdCmp));
for (int i = 0; i < strlen(cmd); i++) {
cmdCmp[i] = cmd[i];
}
FILE *file = fopen(ASSET_FILE, "r");
//loop until target line is reached
while (strcmp(cmdTemp, cmdCmp) != 0) {
//check if last line is read
if (lineIndex == lineCounter(file)-1) {
return -1;
}
memset(cmdTemp, 0, sizeof(cmdTemp));
char line[61];
fgets(line, 61, file);
//set cmdTemp to the command on current line
lineIndex++;
for (int i = 0; line[i] != ':'; i++) {
cmdTemp[i] = line[i];
//return error if line doesn't contain a ':'
if (line[i] = '\n') {
printf("Error: a line in the asset file lacks a ':' separator\n");
exit(1);
}
}
}
return lineIndex;
}
Some context, this function is passed a command, and its job is to read a document that appears like this:
command:aBunchOfInfoOnTheComand
anotherCommand:aBunchOfInfoOnTheComand
and pick out the line that the passed command (cmd[]) is stored on.
The issue is with the fgets on line 24. I have separated the relevant portion of this code out into a smaller test program and it works fine.
The test program that works is:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main (int argc, char *argv[]) {
FILE *file = fopen("tutorInfo.txt", "r");
char line[61];
fgets(line, 61, file);
printf("%s\n", line);
}
The proper exicution of my test program leads me to believe other code in my function is causing the issue, but i'm not sure what. It may be important to note, the problematic code has the same imports as my sample program. Any help would be much appreciated.

Answer 1

As OP didn't provide a Minimal, Complete, and Verifiable example, I have to base my answer on the functional description provided in the question.
I already covered some error and corner cases, but I'm sure I missed some. The approach is also inefficient, as the file is read over and over again, instead of parsing it once and returning a hash/map/directory for easy lookup. In real life code I would use something like GLib instead of wasting my time trying to re-invent the wheel(s)...
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LINE_BUFFER_LENGTH 200
unsigned int locateCmd(FILE *fh, const char *key, const char **cmd_line) {
unsigned int found = 0;
size_t key_length = strlen(key);
*cmd_line = NULL;
/* make sure to start read from start of file */
rewind(fh);
unsigned int line_no = 0;
static char buffer[LINE_BUFFER_LENGTH];
while (!feof(fh) && (found == 0)) {
// NOTE: EOF condition will be checked on the next iteration
fgets(buffer, sizeof(buffer), fh);
size_t length = strlen(buffer);
line_no++;
if (buffer[length - 1] != '\n') {
printf("line %u is too long, aborting!\n", line_no);
return(0);
}
if ((strncmp(key, buffer, key_length) == 0) &&
(buffer[key_length] == ':')) {
found = line_no;
buffer[length - 1] = '\0'; // strip line ending
*cmd_line = &buffer[key_length + 1];
}
}
return(found);
}
int main(int argc, char *argv[]) {
FILE *fh = fopen("dummy.txt", "r");
if (!fh) {
perror("file open");
return(1);
}
int ret = 0;
while (--argc > 0) {
const char *cmd;
const char *key = *++argv;
unsigned line_no = locateCmd(fh, key, &cmd);
if (line_no != 0) {
printf("key '%s' found on line %u: %s\n", key, line_no, cmd);
ret = 0;
} else {
printf("key '%s' not found!\n", key);
};
}
if (fclose(fh) != 0) {
perror("file close");
return(1);
}
return(ret);
}
Test input dummy.txt:
command:aBunchOfInfoOnTheComand
anotherCommand:aBunchOfInfoOnTheComand
brokenline
foo:bar
toolong:sadflkjaLKFJASDJFLKASJDFLKSAJ DLFKJ SLDKJFLKASDFASDFKJASKLDJFLKASJDFLKJASDLKFJASLKDFJLKASDJFLKASJDLFKJASDKLFJKLASDJFLKSAJDFLKJASDLKFJKLASDJFLKASJDFKLJASDLKFJLKASDJFLKASJDFLKJSADLKFJASLKDJFLKC
Some test runs:
$ gcc -Wall -o dummy dummy.c
$ ./dummy command foo bar
key 'command' found on line 1: aBunchOfInfoOnTheComand
key 'foo' found on line 5: bar
line 6 is too long, aborting!
key 'bar' not found!