Basic C cast warning pointer from int

Question

Can someone tell me how to correct this warning/error. I am trying to get just the first character of a string to tell if it a "-".

Error:

grep-lite.c:15:13: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
   if(strcmp((char *) pattern[0],"-") == 0)
             ^
grep-lite.c:29:16: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
   while(strcmp((char *) argv[index][0],"-"))
                ^

Source with warnings/errors:

Line 15:

if (strcmp((char *) pattern[0],"-") == 0)

Line 29:

while (strcmp((char *) argv[index][0],"-"))

Complete Source:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "grep-lite.h"

int main(int argc, char * * argv)
{
  //initailize variables
  int index = 1, lineNumber = 1;
  int oneMatchingLine = FALSE;
  int invertOpt = FALSE, lineNumOpt = FALSE, quietOpt = FALSE;
  char * pattern = argv[argc];

  //check if last arguement is invalid by starting with a '-'
  if(strcmp((char *) pattern[0],"-") == 0)
    {
      error(INVALID_PATTERN);
      return EXIT_ERROR;
    }

  //check if they asked for help
  if(strcmp(argv[index],"--help") == 0)
    {
      printHelpStatement();
      return EXIT_SUCCESS;
    }

    //walk through all options
  while(strcmp((char *) argv[index][0],"-"))
    {
      //find and set option
      if(processOptions(argv[index], &invertOpt, &lineNumOpt, &quietOpt))
    index++;
      //if invalid option fai
      else
    {
      error(INVALID_OPTION);
      return EXIT_ERROR;
    }
    }

  //walk through stdinput searching for pattern relationship
  while(feof(stdin) == 0)
    {
      //initialize
      char * thisLine = NULL;

      // get read line with fgets
      thisLine = fgets(thisLine, MAX_CHARACTERS, stdin);

      //find pattern location in thisLine
      char * patternLoc = strstr(thisLine, pattern);

      //check if we should print this line based of patternLoc and invertOpt
      if((!patternLoc != NULL && !invertOpt) || (pattenLoc == NULL && invertOpt))
    {
      //see if we should print this line
      if(!quietOpt)
        printLine(thisLine, lineNumOpt, lineNumber);
    }
      lineNumber++;
    }

note that `argv[argc]` accesses `argv` out-of-bound (last element is at `argc-1`). — SleuthEye, Feb 27 '15 at 00:13

score 1 · Accepted Answer · edited May 23 '17 at 11:58

1

I will enumerate the problems I find in your code

The correct usage of strcmp() exists in your code, in this line
```
if (strcmp(argv[index],"--help") == 0)
```
strcmp() is intended for string comparison, not character comparison, this
```
if(strcmp((char *) pattern[0],"-") == 0)
```
should be
```
if (pattern[0] == '-')
```
do not cast the variable to force compilation, instead find the actual cause for the compiler error/warning.
You have a severe error, you don't allocate space for the thisLine char pointer, you must allocate memory via malloc() or just declare it as a char array like
```
char thisLine[SOME_CONSTANT_NUMBER];
```
Also, this
```
while(feof(stdin) == 0)
```
is never a good idea instead do it like this
```
char thisLine[100];
while (fgets(thisLine, sizeof(thisLine), stdin) != NULL)
```
You made another very common mistake, arrays in c are indexed from 0 to N - 1, so
```
char *pattern = argv[argc]
```
is wrong, because you are reading one element after the last, the correct code is
```
char *pattern = argv[argc - 1]
```
which will give you the last element.

edited May 23 '17 at 11:58

Community

1
1

answered Feb 27 '15 at 00:10

Iharob Al Asimi

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@napkinsterror I expect your program to crash or something similar if you don't read the updated answer. – Iharob Al Asimi Feb 27 '15 at 00:16
I understand those errors, was just mad I could not correct the basic pointer problem, but thanks for pointing it out. – napkinsterror Feb 27 '15 at 00:17
@napkinsterror don't forget to check `argc` to prevent reading beyond the bounds of `argv`... – Iharob Al Asimi Feb 27 '15 at 00:18
Also, argv[argc] is beyond the end of the array. – Lee Daniel Crocker Feb 27 '15 at 00:21

Basic C cast warning pointer from int

1 Answers1