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 Reference The 1790-1890 Federal Population Censuses: Catalog of National Archives Microfilm (Part 1) National Archives Trust Fund Board National Archives and Records Administration Washington, DC 1993
SoundEx

In our search engine of the fundamental constants, we allow phonetic matches. These phonetic matches were made possible using a modification of an algorithm called "SoundEx," which has been used since the late 19th century to consolidate disparate spellings of surnames in census reports.
First applied to the 1880 census, Soundex is a phonetic index, not a strictly alphabetical one. Its key feature is that it codes surnames (last names) based on the way a name sounds rather than on how it is spelled. For example, surnames that sound the same but are spelled differently, like Smith and Smyth, have the same code and are indexed together. The intent was to help researchers find a surname quickly even though it may have received different spellings. If a name like Cook, though, is spelled Koch or Faust is Phaust, a search for a different set of Soundex codes and cards based on the variation of the surname's first letter is necessary.

This algorithm converts a name to a code (e.g., Michael becomes M240), where the first letter is the first letter of the word, and the numbers represent phonetic parts of latter syllables. Vowels and repeated sounds are ignored. For our purposes, we have an option (-f) which outputs only numbers (e.g., Michael becomes 5240). The code below was adapted for a unix command line environment.
 Soundex Coding Guide 1 = B,P,F,V 2 = C,S,G,J,K,Q,X,Z 3 = D,T 4 = L 5 = M,N 6 = R The letters A,E,I,O,U,Y,H, and W are not coded.

//Soundex code as implemented by Kevin Setter, 8/27/97
//Usage: soundex [-f] <name1> <name2> ...

//-f treats the first character of name just like the others.
//If no names are specified in the arguments, soundex will read
//from the standard input until end of file is encountered.
//Note that names of two characters or less are disregarded.

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

#define MAXNAMELEN 50
#define MAXLINELEN 500

int FullFlag;

//Deletes the first word from a string
char *delfirstword(char *s)
{
char *sout = (char *)malloc(strlen(s));
int i = 0, i2 = 0;

if (s[0] == (char)NULL) return s;
while (isspace(s[i])) i++;
while ((!isspace(s[i])) && (s[i] != (char)NULL)) i++;
if (s[i] == (char)NULL) return "";
while ((isspace(s[i])) && (s[i] != (char)NULL)) i++;
while (s[i] != (char)NULL)
{
sout[i2] = s[i];
i++; i2++;
}
sout[i2] = (char)NULL;
return sout;
}

//Returns the soundex equivalent to In
char *Soundex(char *In)
{
int Iin, Iout;
char C, PrevDig, *Out = (char *)malloc(10);

if (FullFlag)
{Iin = 0; Iout = 0; PrevDig = '*';}
else
{Iin = 1; Iout = 1;
Out[0] = tolower(In[0]); PrevDig = Out[0];}

while ((In[Iin] != (char)NULL) && (Iout <= 4))
{
In[Iin] = tolower(In[Iin]);
switch (In[Iin])
{
case 'b' : C = '1'; break;
case 'p' : C = '1'; break;
case 'f' : C = '1'; break;
case 'v' : C = '1'; break;
case 'c' : C = '2'; break;
case 's' : C = '2'; break;
case 'k' : C = '2'; break;
case 'g' : C = '2'; break;
case 'j' : C = '2'; break;
case 'q' : C = '2'; break;
case 'x' : C = '2'; break;
case 'z' : C = '2'; break;
case 'd' : C = '3'; break;
case 't' : C = '3'; break;
case 'l' : C = '4'; break;
case 'm' : C = '5'; break;
case 'n' : C = '5'; break;
case 'r' : C = '6'; break;
default : C = '*';
}
if ((C != PrevDig) && (C != '*'))
{
Out[Iout] = C;
PrevDig = Out[Iout];
Iout++;
}
Iin++;
}

if (Iout < 4)
for (Iin=Iout; Iin<4; Iin++)
Out[Iin] = '0';

Out[4] = NULL;
return Out;
}

//Main function
int main(int argc, char *argv[])
{
char *Name = (char *)malloc(MAXNAMELEN), *Line = (char *)malloc(MAXLINELEN);
int I;

FullFlag = 0;

if (argc >= 2)
{
if (!strcmp(argv[1], "-f"))
FullFlag = 1;
if ((!strcmp(argv[1], "-h")) || (!strcmp(argv[1], "-?")) ||
(!strcmp(argv[1], "?")))
{
printf("\nSoundex code as implemented by Kevin Setter, 8/27/97\n");
printf("Usage: soundex [-f] <name1> <name2> ...\n\n");
printf("-f treats the first character of name just like the others.\n");
printf("If no names are specified in the arguments, soundex will read\n");
printf("from the standard input until end of file is encountered.\n");
printf("Note that names of two characters or less are disregarded.\n");
}
}

if (FullFlag && (argc >= 3))
{
for (I=2; I<=(argc-1); I++)
if (strlen(argv[I]) >= 3)
printf("%s ", Soundex(argv[I]));
printf("\n");
return 0;
}
if ((!FullFlag) && (argc >= 2))
{
for (I=1; I<=(argc-1); I++)
if (strlen(argv[I]) >= 3)
printf("%s ", Soundex(argv[I]));
printf("\n");
return 0;
}

while (gets(Line) != NULL)
{
while (strcmp(Line, ""))
{
sscanf(Line, "%s", Name);
if (strlen(Name) >= 3)
printf("%s ", Soundex(Name));
strcpy(Line, delfirstword(Line));
}
printf ("\n");
}

free(Line); free(Name);
return 0;
}