How to find size of command line arguments?

Question about C , is `argv' 8 bytes? Asking because I'm trying to find the sizeof of my command line arguments. It's returning 8 bytes, but was expecting 1, since I read that all command line args are chars. Here's the code I wrote:

Code:

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#include <stdio.h>


int main(int argc, char* argv[]) {
// User enters parameters for the argument
// Get the argument for argv[1], read in the key in that positon of the argument
printf("\nThis is the first argument after the program name: %s\n", argv[1]);
// Get the type
printf("\nThis is the size of the first argument: %ld\n", sizeof(argv[1]));
}

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Here's my output:


This is the first argument after the program name: 5


This is the size of the first argument: 8

We still haven't covered pointers yet in my class, that's the next lesson

Quote:

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but was expecting 1, since I read that all command line args are chars.

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The command line arguments are an array of C-strings not single characters.

What did you enter for your command line arguments? What is the value of argc?

To find the length in characters use strlen
Note: strlen does not count the zero byte at the end.

Tim S.

Quote:

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Originally Posted by jimblumberg

The command line arguments are an array of C-strings not single characters.

What did you enter for your command line arguments? What is the value of argc?

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Thank you for your reply. I entered: ./main 5
And the output was 8.

argv is an array of pointers.
sizeof returns the size of its argument type.
The size of pointers on your system is 8 bytes (i.e., you are on a 64-bit system), so sizeof is returning 8.

To get the size of a string, you need to use strlen, which counts the number of characters up to (but not including) the first '\0' character in the string. I.e., it basically does this:

Code:

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size_t my_strlen(const char *str)
{
    const char *p = str;
    while (*p != '\0')
        ++p;
    return p - str; // return difference between final position
                    // and initial position of p.
}

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Note that both sizeof and strlen return a size_t argument, so to print it you either need to use the proper format specifier ("%zu"), or you need to cast the value to match the format specifier that you use.

Code:

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printf("%zu\n", strlen(argv[1]));
printf("%d\n", (int)strlen(argv[1]));
printf("%ld\n", (long)strlen(argv[1]));

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The following program prints the sizes and values of all of the arguments passed on the command line:

Code:

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#include <stdio.h>
#include <string.h>
 
int main(int argc, char **argv)
{
    for (int i = 0; i < argc; ++i)
        printf("%2d: %s\n", (int)strlen(argv[i]), argv[i]);
    return 0;
}

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