Array C programming: source code sample for simple C arrays.

How to read lines of a text file into a very simple fixed size array. Also shows how to sort the array content alphabetically, and how to write array content as another text file.

/*
 C array source code example:
 - read text file into a simple array
 - with fixed maximum number of lines
 - with fixed maximum line size
 - sort the array
 - write array content into another text file.
*/
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
// how many text lines can this program read?
#define MAX_TEXT_LINES 1000 // up to 1000 lines
#define MAX_LINE_LENGTH 200 // with up to 200 chars each
// very simple static array for text storage:
char aTextData[MAX_TEXT_LINES+10][MAX_LINE_LENGTH+10];
// +10 are safety spaces, to avoid crash on off-by-one errors.
// tell that these functions exist further below:
int perr(const char *pszFormat, ...);
int processData(char aText[MAX_TEXT_LINES+10][MAX_LINE_LENGTH+10],
 int iLinesUsed, int iLinesAlloced);
int main(int argc, char *argv[])
{
 if (argc < 3)
 return 9+perr("specify input and output filename.\n");
 char *pszInFile = argv[1];
 char *pszOutFile = argv[2];
 int iTextSize = MAX_TEXT_LINES; // how large is the array
 int iTextUsed = 0; // how many lines contained
 // safety: clean the memory with zeros
 memset(aTextData, 0, sizeof(aTextData));
 // line buffer for reading
 char szLineBuf[MAX_LINE_LENGTH+10];
 memset(szLineBuf, 0, sizeof(szLineBuf));
 // read input file into the array. use binary mode "rb"
 // to avoid CR/LF line end conversions.
 FILE *fin = fopen(pszInFile , "rb");
 if (!fin)
 return 9+perr("cannot read %s\n", pszInFile);
 // while not end of file, read another line
 while (fgets(szLineBuf, sizeof(szLineBuf)-10, fin) != 0)
 {
 // check if array has space for another line
 if (iTextUsed >= iTextSize)
 { perr("overflow: too many text lines\n"); break; }
 // strip CR/LF from line endings so we get pure text
 char *psz = strchr(szLineBuf, '\r'); if (psz) *psz = '0円';
 psz = strchr(szLineBuf, '\n'); if (psz) *psz = '0円';
 // store the line
 strncpy(aTextData[iTextUsed], szLineBuf, MAX_LINE_LENGTH);
 aTextData[iTextUsed][MAX_LINE_LENGTH-1] = '0円'; // safety
 iTextUsed++;
 }
 fclose(fin);
 // do some processing on the array contents
 processData(aTextData, iTextUsed, iTextSize);
 // write the whole array to output file. use text mode "w"
 // so under windows it will create CRLF line endings.
 FILE *fout = fopen(pszOutFile, "w");
 if (!fout)
 return 9+perr("cannot write %s\n", pszOutFile);
 int iLine;
 for (iLine=0; iLine<iTextUsed; iLine++)
 {
 strncpy(szLineBuf, aTextData[iLine], MAX_LINE_LENGTH);
 szLineBuf[MAX_LINE_LENGTH-2] = '0円'; // safety w/ space for LF
 strcat(szLineBuf, "\n"); // produces CRLF under windows
 int nlen = strlen(szLineBuf);
 if (fwrite(szLineBuf, 1, nlen, fout) != nlen)
 return 9+perr("failed to fully write %s\n", pszOutFile);
 }
 fclose(fout);
 return 0;
}
// processing example: sort array text lines alphabetically
// with the simplest possible sorting algorithm (bubblesort).
int processData(char aText[MAX_TEXT_LINES+10][MAX_LINE_LENGTH+10],
 int iLinesUsed, int iLinesAlloced)
{
 int iOuterIdx, iInnerIdx;
 char aBuffer[MAX_LINE_LENGTH+10];
 for (iOuterIdx=0; iOuterIdx<iLinesUsed; iOuterIdx++)
 {
 for (iInnerIdx=iOuterIdx+1; iInnerIdx<iLinesUsed; iInnerIdx++)
 {
 char *pszLine1 = aText[iOuterIdx];
 char *pszLine2 = aText[iInnerIdx];
 if (strcmp(pszLine1, pszLine2) > 0)
 {
 // swap both lines
 strcpy(aBuffer, pszLine1);
 strcpy(pszLine1, pszLine2);
 strcpy(pszLine2, aBuffer);
 }
 }
 }
 printf("sorted %d lines.\n", iLinesUsed);
 return 0;
}
// helper function: print error with variable parameters.
int perr(const char *pszFormat, ...)
{
 va_list argList;
 va_start(argList, pszFormat);
 char szBuf[1024];
 vsprintf(szBuf, pszFormat, argList);
 fprintf(stderr, "error: %s", szBuf);
 return 0;
}

// See also: C example for variable sized array .

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