Just wondering what happens when I use the wrong format specifier in C?
For example:
x = 'A'; printf("%c\n", x); printf("%d\n", x); x = 65; printf("%c\n", x); printf("%d\n", x); x = 128; printf("%d\n", x); 
2 Answers
what happens when I use the wrong format specifier in C?
Generally speaking, undefined behaviour.*
However, recall that printf is a variadic function, and that the arguments to variadic functions undergo the default argument promotions. So for instance, a char is promoted to an int. So in practice, these will both give the same results:
char x = 'A'; printf("%c\n", x); int y = 'A'; printf("%c\n", y); whereas this is undefined behaviour:
long z = 'A'; printf("%c\n", z); * See for example section 7.19.6.1 p9 of the C99 standard:
If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.
answered May 31, 2013 at 19:33
Oliver Charlesworth
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since x is A, the first print f will print: 'A'.
The second will print the ascii value of A (look it up).
The 3rd one will print the ascii character for 65 (I think this is A or a, but its a letter).
The fourth one will print 65.
The 5th one will print 128.
1 Comment
Antti Haapala
The behaviour will completely depend on type of
x (which is not specified in the question itself).
xthis is impossible to answer.