Reading ASCII numbers using "D" instead of "E" for scientific notation using C

Question

I have a list of numbers which looks like this: 1.234D+1 or 1.234D-02. I want to read the file using C. The function atof will merely ignore the D and translate only the mantissa.

The function fscanf will not accept the format '%10.6e' because it expects an E instead of a D in the exponent.

When I ran into this problem in Python, I gave up and merely used a string substitution before converting from string to float. But in C, I am sure there must be another way.

So, how would you read a file with numbers using D instead of E for scientific notation? Notice that I do not mean how to read the strings themselves, but rather how to convert them to floats.

Thanks.

Sinan Ünür · Accepted Answer · 2010-03-31T18:25:49.540

2

You can take advantage of strtod and strtok:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void) {
    char in[] = "1.234D+1 ABCD 1.234D-02 5\n";
    char *cursor;
    char *endp;
    for ( cursor = strtok(in, " "); cursor; cursor = strtok(NULL, " ")) {
        double d = strtod(cursor, &endp);
        if ( *endp == 'D' ) {
            *endp = 'e';
            d = strtod(cursor, &endp);
        }
        if ( endp != cursor ) {
            printf("%e\n", d);
        }
    }
    return 0;
}

Output:

E:\> cnv
1.234000e+001
1.234000e-002
5.000000e+000

edited Mar 31 '10 at 18:25

answered Mar 31 '10 at 17:42

Sinan Ünür

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I am disappointed that C lacks native support for reading scientific notation using `D` instead of `E`. Your proposed code is the closest to a perfect solution. Thanks! – Escualo Apr 01 '10 at 17:05
3

@Arrieta: I am disappointed it can't parse numbers where the letter Q appears instead of the numeral 0 (zero). Seems the library designers didn't understand how essential our requirements are for so many programs... ;-) – Tony Delroy Jun 22 '12 at 12:14

score 1 · Answer 2 · answered Mar 31 '10 at 17:33

1

replace D with E, by looping along string. then atof.

answered Mar 31 '10 at 17:33

Andrey

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score 0 · Answer 3 · answered May 20 '14 at 05:47

Here this function is to replace "D" into "E" in the scientific notation with "D".

std::string dToE(string cppstr)
{
    str1.replace(cppstr.find("D"),1,"E");
    return cppstr;
}

If the C string for scientific notation is defined by: char * cstr = "1.2D+03"; or usually obtained by strtok method, which returns C string, then use atof(dToE(string(cstr)).c_str()) to get the scientific notation with "E".

Since atof only accept C style string, you should use c_str() string method to convert C++ string into C string.

Reading ASCII numbers using "D" instead of "E" for scientific notation using C

3 Answers3

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