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Fast but unchecked - C
Revision of C example from a Well House Consultants training course
More on Revision of C [link]
Source code: overflow.c Module: C230
#include <stdio.h>
/* Some features of C that make it fast to run but you have to be very sure that your code is right!*/ /* Note for reader - please see associated blog article. This shows you things that can go wrong and you should not do! */ int main() { /* Overflow of integers */ short int a = 40000; short int b = 30000; short int c; c = a+b; printf("First Value is %d\n",c); /* failing to initialise */ float empty; printf("Unset value is %f\n",empty); /* Accessing an array beyond its scope */ int k; int d1[] = {666,777}; int numbers[] = {4,7,9,15}; int d2[] = {888,999}; for (k=-2;k<7;k++) { numbers[k] = numbers[k+1]; } for (k=-2;k<7;k++) { printf("Array contains is %d\n",numbers[k]); } /* Uninitialised pointers */ int *somewhere; printf("Final Value is %d\n",*somewhere); /* Output using the wrong format (at least you often get a warning) */ float pie = 3.1415; printf("Floated pie value is %d\n",pie); /* Accessing character strings out of scope */ char *wordy = "Fishpaste"; wordy[9] = '*'; printf("Overshooting %s\n",wordy); } /* Sample output WomanWithCat:harwell grahamellis$ ./overflow First Value is 4464 Unset value is 0.000000 Array contains is 999 Array contains is 4 Array contains is 7 Array contains is 9 Array contains is 15 Array contains is 0 Array contains is 0 Array contains is 0 Array contains is 666 Final Value is -17958193 Floated pie value is 3072 Bus error: 10 WomanWithCat:harwell grahamellis$ */ Learn about this subject
This module and example are covered on the following public courses:
* Learning to program in C and C++ * C++ for C Programmers * C and C++ Programming * Learning to program in C and C++ * C and C++ Programming Also available on on site courses for larger groups Books covering this topic
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This example comes from our "Revision of C" training module. You'll find a description of the topic and some
other closely related examples on the "Revision of C" module index page.
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