CODEWITHSUNDEEP
cstringfloating-pointtoken
Rory Thoman
Rory Thoman

Reputation: 69

strtof() producing weird results in C

first of all, compiling with flags -Wall, -ansi, -pedantic. no warnings or errors. and no debugging is helping.

basically my code is working fine however returning very weird and unexpected results when I turn a token from a string to a float using strtof()

the section of code below is:

 printf("token is %s\n", token);
 newstockdata->unitPrice = strtof(token, NULL);
 printf("price is %d\n", newstockdata->unitPrice);

newstockdata is allocated to the correct size: unitPrice is a float variable: the first printf statement prints "150.00": the second printf statement prints "0" but after a few iterations it returns a really long consistent number. any help please?

Upvotes: 0

Views: 490

Answers (2)

M.M
M.M

Reputation: 141618

The problem is here, assuming that unitPrice is a float:

printf("price is %d\n", newstockdata->unitPrice);

To print a float you must use the %f specifier. Otherwise, it is undefined behaviour and anything could happen.

A possible explanation of the changing values you see might be that your system passes floats in a different register to ints. The printf receiving %d is looking in a register that is never set, so you are seeing whatever value was left over from some previous operation.

This is actually pretty common, here is an example - %esi is used for the int, and %xmm0 is used for the floating-point value.

Upvotes: 4

Kishore
Kishore

Reputation: 839

You have to handle overflow cases. After calling strtof() check errno for overflow. If you think the values could be very long, you can use double or long double.

Upvotes: -1

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