Why is my output of strings in C not correct?

Question

I'm trying to use uart_poll_out instead of printk with my program and before with printk I was able to get the correct output I wanted to my uart console. Here was the code and correct output:

    for (int i = 0; i < sizeof cmd_handles / sizeof cmd_handles[0]; i++)
    {
        printk("%s\t%s\n", cmd_handles[i].cmd, cmd_handles[i].help);
    }

help    Show commands and descriptions
sample  sample function

Now I have to use uart_poll_out and my output is messed up. I don't know how to fix it/what is wrong with it. Here is my code and (incorrect) output. I want the output to look the same as above.

    for (int i = 0; i < sizeof cmd_handles / sizeof cmd_handles[0]; i++)
    {
        u8_t tempbuff[1];
        u8_t buf[sizeof(cmd_handles[i].cmd) + sizeof(cmd_handles[i].help) + 5]; // the 5 is arbitrary
        sprintf(buf, "%s\t%s\n", cmd_handles[i].cmd, cmd_handles[i].help);
        for (int i = 0; i < sizeof(buf); i++)
        {
            uart_poll_out(comm_uart, buf[i]);
        }
    }

help    Show comsample  sample

This is cmd_handles:

const cli_cmd_handle_t cmd_handles[] =
{
    {.cmd = "help", .help = "Show commands and descriptions", .handler = cli_help_handler},
    {.cmd = "sample", .help = "sample function", .handler = sample_function},
};

Does anyone know how to fix this? Thanks :)

Edit: definition of cli_cmd_handle_t:

{
    const char *cmd;
    const char *help;
    CliCmdHandler handler;
} cli_cmd_handle_t;```

@FredLarson Thanks, that kind of helped. Now my output is `help Show comsample sample` which is closer haha. I'll update my post. — PurpleSpark, Jul 16 '20 at 16:12
Please show the `struct` definition so we know that `sizeof(cmd_handles[i].cmd)` gives you the size of an array, not that of a pointer. BTW don't forget to allow room for a null terminator. — Weather Vane, Jul 16 '20 at 16:13
I don't think you want to use an arbitrary size for `buf` because you use `sizeof(buf)` in your loop condition, so you are sending random junk to `uart_poll_out()`. — Fred Larson, Jul 16 '20 at 16:15
Yes, `sizeof(cmd_handles[i].cmd)` is the size of a pointer, not the data it points to. — Weather Vane, Jul 16 '20 at 16:19
@FredLarson Actually `sizeof("\t\n")` is 3. It's `sizeof(cmd_handles[i].cmd)` and `help` that's the problem. — user253751, Jul 16 '20 at 16:46
@user253751: Yes, [you are correct](https://stackoverflow.com/q/2245664/10077). — Fred Larson, Jul 16 '20 at 16:51
`for (int i = 0; i < sizeof(buf); i++)` --> `for (int i = 0; buf[i]; i++)` — chux - Reinstate Monica, Jul 17 '20 at 05:15

score 0 · Accepted Answer · answered Jul 17 '20 at 04:11

0

Thanks @WeatherVane for helping. I had to use strlen() instead of sizeof() to get the correct output.

answered Jul 17 '20 at 04:11

PurpleSpark

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Why is my output of strings in C not correct?

1 Answers1