CODEWITHSUNDEEP
cstring
Geralt
Geralt

Reputation: 123

Why doesn't strtod work in the correct way?

I am coding in Code-Blocks Editor with GNU GCC Compiler.I tried to use function strtod which the below prototype:

double strtod(const char *a, char **b);

If I use the below code:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main() {
    char *a;
    a="99.5HELLO";
    char *b;
    printf("%.1lf\n%s", strtod(a, &b), b);
    return 0;
}

I expect the Console Terminal to represent something like this after running the code:

99.5
HELLO

But what I actually got was something strange:

99.5
@

What's happening? Where did I make a mistake?

Upvotes: 2

Views: 347

Answers (1)

Kerrek SB
Kerrek SB

Reputation: 477140

The order of evaluation of subexpressions is unspecified, and so the last function argument may be evaluated first and you end up reading the uninitialized value b, which is undefined behaviour.

Order the evaluations:

const char *a = "99.5HELLO";
char *b;
double d = strtod(a, &b);

printf("%.1f\n%s", d, b);

Upvotes: 8

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