CODEWITHSUNDEEP
clinuxargumentscommand-line-argumentsargument-passing
rzrscm
rzrscm

Reputation: 89

What's the correct way to convert an argument passed to a program to a long double variable?

I'm having trouble with this...It compiles, but segfaults immediately when run...Using GDB, I determined that it segfaults while trying to initiate the long doubles. I feel like atoi might be the wrong function to use, but I tried other similar functions and still got a segfault.

int main(int argc, char *argv[]) {
  long double x = atoi(argv[1]);
  char oper = argv[2][0];
  long double y = atoi(argv[3]);

Upvotes: 0

Views: 146

Answers (3)

Carl Norum
Carl Norum

Reputation: 225042

atoi() stands for "ascii to integer", which isn't what you want. You should use an appropriate function — strtold(3) is most appropriate, but you can probably use sscanf(3), too.

Upvotes: 4

Kerrek SB
Kerrek SB

Reputation: 477368

Use strtold:

#include <stdlib.h>
#include <errno.h>

char * e;
errno = 0;
long double d = strtold(argv[1], &e);

if (*e != 0 || errno != 0) { /* Error! Do not consume the result. */ }

// result now in "d"

You can use the value of *e to figure out whether any part of the string was consumed; see the manual for details. My example just checks whether the entire string could be parsed.

I'm actually not sure if there's a thread-safe solution... (Oh, I think it is, because errno is thread-local.)

Upvotes: 2

Daniel Fischer
Daniel Fischer

Reputation: 183968

The correct way to convert a string to a long double is

long double strtold(const char *nptr, char **endptr);

Upvotes: 2

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