Eagle Eagle - 4 months ago 87
C Question

Using the builtin function __builtin_add_overflow_p in gcc

I was wondering on how to use this function, because I get an error when I do this:

#define INT_ADD_OVERFLOW_P(a, b) \
__builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0);
#include <stdio.h>
#include <assert.h>
__int main()
{
int x1 = -1073741826;
int y1 = -1073741826;
int z1 = x1+y1;
INT_ADD_OVERFLOW_P ( x1, y1);
printf("%d\n",z1);
return 0;
}


Compile_OUTPUT:

gcc -c -Wall -D DEBUG tempFile.c
gcc tempFile.o -o tempFile
Makefile:8: recipe for target 'tempFile' failed//new error after update


Compile_ERROR:

tempFile.c: In function ‘main’:
tempFile.c:10:1: warning: implicit declaration of function ‘__builtin_add_overflow_p’ [-Wimplicit-function-declaration]
tempFile.o: In function `main':
tempFile.c:(.text+0x44): undefined reference to `__builtin_add_overflow_p'
collect2: ld returned 1 exit status
make: *** [tempFile] Error 1


Here is a link to the functions I want to use:

https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html

Here is the makefile that i'm using:

compiler=gcc
CFLAGS=-c -Wall -D DEBUG
programname=tempFile

all: $(programname)

$(programname): $(programname).o
$(compiler) $(programname).o -o $(programname)

$(programname).o: $(programname).c
$(compiler) $(CFLAGS) $(programname).c

clean:
rm *o $(programname)

Answer

So I figured out how to use the built-in functions. Instead of using __builtin_add_overflow_p I used __builtin_add_overflow

#include <stdio.h>
#include <assert.h>
int main()
  {
  int x1 = -1073741826;
  int y1 = -1073741826;
  int z1 = x1+y1; 
  int temp;
  printf("%d\n",__builtin_add_overflow ( x1,  y1, &temp));
  if(__builtin_add_overflow ( x1,  y1, &temp)){
    printf("overflow detected");
  }
  printf("%d\n",z1);
  return 0;
}
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