Struct Array Segmentation Fault

Question

I keep running into a problem with reading values of a struct array, where I keep getting a segmentation fault. Here is the code:

int main() 
{
    /* Get PATH Environment Variable */
    char *pathv[MAX_PATHS];
    char cmd_line[MAX_ARGS];
    struct command_t cmd[3];         //THIS IS THE STRUCT ARRAY
    size_t len = 0;

    /* Parse The Path */
    ParsePath(pathv);

    while(1) {

        /* Print Continuous Prompt */
        PrintPrompt();

        /* Read Command Line & Parse It */
        ReadCommand(cmd_line);

        ParseCommand(cmd_line, cmd);    //PASSING IT TO THIS METHOD
    }

    return 0;
}



int ParseCommand(char *buffer, struct command_t *cmd)
{
    char *name = "Test";
    cmd[0].name;  //IF THIS IS COMMENTED OUT AND THE OTHER LINE AS WELL, PROGRAM RUNS
    printf("%s\n", cmd[0].name); //FINE....THESE TWO LINES CAUSE SEG. FAULT
}



struct command_t {
    char *name;
    int argc;
    char *argv[MAX_ARGS];
};

What am I doing wrong? Your help is greatly appreciated.

You might also like to show us the definition of struct command_t. — alk
– alk, Commented Oct 20, 2013 at 18:05
Sorry, I just added my struct code. This struct is in a separate header file! — Jake Z
– Jake Z, Commented Oct 20, 2013 at 18:19

shf301 · Accepted Answer · 2013-10-20 18:06:16Z

2

You never initialize cmd nor write any data. Accessed uninitialized data is undefined behavior in C so yes it is valid to crash. You need to write something into cmd[0].name before reading from it.

answered Oct 20, 2013 at 18:06

shf301

31.5k2 gold badges57 silver badges88 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jake Z Over a year ago

I'm an idiot. I found out what the problem was...I forgot to put = name...WOW. Sorry guys! Thank you.

Havenard · Accepted Answer · 2020-07-08 20:33:15Z

1

In C, when you declare a variable without assigning a value to it doesn't mean it is empty. It may point to memory garbage from stuff that was ran previously.

Your attempt to printf() whats in cmd[0].name without initializing it can be catastrophic.

You should initialize each variable in your struct before trying to access its value, or at least zero-fill everything in order to make it safe to read:

memset(cmd, 0, sizeof(*cmd) * 3);

edited Jul 8, 2020 at 20:33

answered Oct 20, 2013 at 18:13

Havenard

28.1k5 gold badges38 silver badges66 bronze badges

2 Comments

mLstudent33 Over a year ago

Isn't zero-filling memset(cmd, sizeof(*cmd), 0)?

Havenard Over a year ago

@mLstudent33 Not quite, but yes, forgot a parameter there.

Collectives™ on Stack Overflow

Struct Array Segmentation Fault

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related