Cannot print or access char * inside a function - c

Question

The code below does not print nor return the char * temp which I am trying to retrieve from a text file containing a matrix of the form:
4
spQ77377.1 0.000000 0.776030 0.781073 0.804880
spO91086.1 0.776030 0.000000 0.564157 0.559756
spP04578.2 0.781073 0.564157 0.000000 0.302724
spO12164.1 0.804880 0.559756 0.302724 0.000000
The whole code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
char * const getField( char lineBuffer[255], int field ) {
printf( "\n " );
static char temp[30];
int f = 0;
for( int i = 0; lineBuffer[i]!='\n' ; i++ ) {
if( f == field && lineBuffer[i] != ' ' ) {
temp[i] = lineBuffer[i];
printf( "%c", temp[i] );
}
if( lineBuffer[i] == ' ' && lineBuffer[i+1] == ' ' ) {
printf( "||" );
f++;
}
if( f > field ) {
printf( " break " );
printf( "*%s*", temp );
fflush(stdout);
return temp;
}
}
return "!";
}
int main() {
FILE *matrixStream;
matrixStream = fopen( "outfile", "r" );
if ( matrixStream == NULL ) {
printf( "\n\tERROR FILE NOT FOUND!\n" );
exit( 1 );
}
char lineBuffer[255];
fseek( matrixStream, 0, SEEK_SET );
int line = 0;
char ** field1 = malloc( 4 * sizeof( char *) );
while( fgets( lineBuffer, 255, matrixStream ) ) {
if( line != 0 ) {
printf( "\n line = %d ", line-1 );
if( line == 1 ) {
field1[line-1] = malloc( 30 * sizeof( char ) );
strcpy( field1[line-1], getField( lineBuffer, 1 ) );
}
}
line++;
}
printf( "\n" );
fclose( matrixStream );
return 0;
}
My objective is to have the function getField() to return a certain field or column (provided in argument as int field) for a line in the matrix.
For now, I only have the following output and can not seem to understand the problem, there are no error message during compilation with the options -Wall -pedantic. Here is the exact output:
line = 0
||0.000000|| break **
line = 1
line = 2
line = 3
The value of char * temp is not printed between the * characters as it should be.
Thank you in advance for any help or advice you can provide.

Answer 1

you need to terminate your temp buffer, and to have 2 indexes
static char temp[30];
int toff = 0; // temp offset
int f = 0;
for( int i = 0; lineBuffer[i]!='\n' ; i++ ) {
if( f == field && lineBuffer[i] != ' ' ) {
temp[toff++] = lineBuffer[i]; // use temp offset
printf( "%c", temp[i] );
}
if( lineBuffer[i] == ' ' && lineBuffer[i+1] == ' ' ) {
printf( "||" );
f++;
}
if( f > field ) {
temp[toff] = 0; // 0 terminate
printf( " break " );
printf( "*%s*", temp );
fflush(stdout);
return temp;
}
}
of course you should also error out if toff > sizeof(temp)
BTW the reason you get nothing is that temp, being static, is initialized to 0 at startup and you never write anything to temp[0] (beacuse you use the line buffer offset). So temp is an empty string always