runtime error with malloc - c

Question

#define MAXL 256
I think the problem with my code is that eventho numInput = 3, somehow, output[2] did not exist so that when I try to assign it, the program crash (just guessing).
Is there a way to check if ouput[2] exist? or maybe someone will be able to find out the real problem of my code, that would be awesome!
Any help would be greatly appreciated!
NOTE: The reason that I cast malloc is that it is expected by my lecturer.
Input strings are: 25 7 * 14 - 6 +
1 24 3 + * 41 -
2 37 4 + * 15 +
void processPostfixExp(const char * fileName)
{
char ** input = NULL;
double ** output = NULL;
int i = 0, numInput = 0;
char tempInput[MAXL] = {0};
FILE * pFile = NULL;
/* Get number of strings, check if file is readable and open file */
numInput = checkFile(fileName);
pFile = fopen(fileName, "r");
/* Allocate memory for the string storages and alert if fail */
input = (char**)malloc(numInput * sizeof(char*));
output = (double**)malloc(numInput * sizeof(double*));
if(!input || !output)
{
printf("Memory allocation failed.\n");
system("PAUSE");
exit(1);
}
/* Scan the file by lines and duplicate the string to input storage */
for(i = 0; i < numInput; ++i)
{
fgets(tempInput, MAXL, pFile);
tempInput[strlen(tempInput)-1] = '\0';
input[i] = strdup(tempInput);
//printf("\n%s", input[i]);
}
/* Close file and clear screen */
fclose(pFile);
system("CLS");
/* Call converter and display result */
printf("-------------------------------------------------------\n");
printf("\nPostfix expression evaluation:\n");
for(i = 0; i < numInput; ++i)
{
printf("input = %s", input[i]); /* i = 2 Printf SUCCESS */
*output[i] = evaluatePost(input[i]); /* i = 2 CRASH HERE */
/* I added a check at the top most of the evaluatePost(), program did not get to there */
//printf("\nCase %d: %s\nResult:%.2f\n", i + 1, input[i], *output[i]);
}
printf("\n");
printf("-------------------------------------------------------\n");
}
UPDATE:
so I added these lines and can confirm that output[2] does not exist... how is that possible? Please help, Thank you!
for(i = 0; i < numInput; ++i)
{
*output[i] = (double)i;
printf("output[%d] = %.1f\n", i, *output[i]);
}

Answer 1

The problem is that you have:
*output[i]
You have allocated numInput pointers to double, but the pointers themselves don't exist.
It looks like you want to allocate space not for pointers, but for doubles:
double *output;
…
output = (double*)malloc(numInput * sizeof(double));

Answer 2

I'm not sure what is wrong with your call to evaluatePost(), especially as you have not provided a prototype for that function.
However, overall, your code should look similar to the following:
in the future, please post code that (standalone) actually cleanly compiles
when you want help with a run time problem.
strongly suggest compiling with all warnings enabled.
For gcc, at a minimum, use '-Wall -Wextra -pedantic'
When handling a error, always cleanup allocated memory, open files, etc.
#define _POSIX_C_SOURCE (200809L)
#include <stdio.h>
#include <stdlib.h> // exit() and EXIT_FAILURE
#include <string.h> // memset() and strdup()
#define MAXL (256)
// prototypes
int checkFile( const char * );
double evaluatePost( char * );
void processPostfixExp(const char * fileName)
{
char **input = NULL;
double **output = NULL;
int i = 0;
int numInput = 0;
char tempInput[MAXL] = {0};
FILE *pFile = NULL;
/* Get number of strings, check if file is readable and open file */
numInput = checkFile(fileName);
if( NULL == (pFile = fopen(fileName, "r") ) )
{ // then fopen failed
perror( "fopen for input file failed" );
exit( EXIT_FAILURE );
}
/* Allocate memory for the string storages and alert if fail */
if( NULL == (input = malloc(numInput * sizeof(char*)) ) )
{ // then malloc failed
perror( "malloc for input failed" );
fclose( pFile );
exit( EXIT_FAILURE );
}
// implied else, malloc successful
memset( input, 0x00, numInput*sizeof(char*) ); // to make later free() operation easy
if( NULL == (output = malloc(numInput * sizeof(double*)) ) )
{ // then malloc failed
perror( "malloc for output failed" );
fclose( pFile );
free( input );
exit( EXIT_FAILURE );
}
// implied else, malloc successful
memset( output, 0x00, numInput * sizeof(double*) ); // to make later free() operation easy
/* Scan the file by lines and duplicate the string to input storage */
for(i = 0; i < numInput; ++i)
{
if( NULL == fgets(tempInput, MAXL, pFile) )
{ // then fgets failed
perror( "fgets for input file failed" );
fclose( pFile );
for( int j=0; j<numInput; j++ )
{
free( input[j] );
free( output[j] );
}
free( input );
free( output );
exit( EXIT_FAILURE );
}
// implied else, fgets successful
char * offset = NULL;
if( NULL != (offset = strstr( tempInput, "\n" )) )
{ // then newline found
*offset = '\0';
}
if( NULL == (input[i] = strdup(tempInput) ) )
{ // then strdup failed
perror( "strdup for input line failed" );
fclose( pFile );
for( int j=0; j<numInput; j++ )
{
free( input[j] );
free( output[j] );
}
free( input );
free( output );
exit( EXIT_FAILURE );
}
//printf("\n%s", input[i]);
} // end for
/* Close file and clear screen */
fclose(pFile);
system("CLS");
/* Call converter and display result */
printf("-------------------------------------------------------\n");
printf("\nPostfix expression evaluation:\n");
for(i = 0; i < numInput; ++i)
{
printf("input = %s", input[i]); /* i = 2 Printf SUCCESS */
*output[i] = evaluatePost(input[i]); /* i = 2 CRASH HERE */
/* I added a check at the top most of the evaluatePost(), program did not get to there */
//printf("\nCase %d: %s\nResult:%.2f\n", i + 1, input[i], *output[i]);
}
printf("\n");
printf("-------------------------------------------------------\n");
for( int j=0; j<numInput; j++ )
{
free( input[j] );
free( output[j] );
}
free( input );
free( output );
} // end function: processPostfixExp