Why does using the wrong format specifier in C crash my program on Windows 7?

Question

My program is as follows;

#include 
#include 

int main()
{
        char string[] = \"Gentlemen start your engines!\";
                


        

Answer 1

Using incorrect format specifier in printf() invokes Undefined Behaviour. Correct format specifier should be %zu (not %d) because the return type of strlen() is size_t

Note: Length modifier z in %zu represents an integer of length same as size_t

Answer 2

You have wrong format specifier. %s is used for strings but you are passing size_t (strlen(string)). Using incorrect format specifier in printf() invokes undefined behaviour. Use %zu instead because the return type of strlen() is size_t.

So change

 printf("That string is %s characters long.\r\n", strlen(string));

to:

 printf("That string is %zu characters long.\r\n", strlen(string));

Since you are using gcc have a look here for more info what can be passed to printf

Answer 3

You have a problem here printf("That string is %s characters long.\r\n", strlen(string));

put

printf("That string is %d characters long.\r\n", strlen(string)); %d because you want to printthe length of str (strlen returns number)

Answer 4

Program crashes because formatting routine tries to access a string at address 0x0000001D which is the result of strlen() where is nothing like a string and likely there's no acessible memory at all.

Answer 5

 printf("That string is %d characters long.\r\n", strlen(string));

instead:

 printf("That string is %s characters long.\r\n", strlen(string));