Surviving C and PostgreSQL

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Surviving C and PostgreSQL

• CS186 Supplemental Session
• 9/13/04
• Matt Denny, Paul Huang, Murali Rangan
• (Originally prepared by Shariq Rizvi, Wei Xu,
  Shawn Jeffery)

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Outline

• A Review of C
• PostgreSQL Basics
• Tour of Assignment 1
• 2Q

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A Review of C

• Review Pitfalls of C Programming for Java
  Programmers
• Pointers and Arrays
• Strings
• Segmentation Faults
• For more information, consult The C
  Programming Language by Kernighan and Ritchie or
  tutorial on web site

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• Pointer variable containing address of another
  variable
• float f / data variable /
• float f_addr / pointer variable /
• f_addr f / address operator /

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f_addr 3.2 / indirection operator
/ float gf_addr /
indirectiong is now 3.2 / f 1.3
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Arrays and Pointers
int month12 / month is a pointer to base
address 430 system allocates
12sizeof(int) bytes at 430
/ month3 7 / integer at address
(4303sizeof(int)) is now 7
/ ptr month 2 / ptr points to month2,
i.e. ptr (4302 sizeof(int))
438 / ptr5 12 / int at
address (4345sizeof(int)) is
now 12 same as month7 /

• Now , month6, (month6), (month4)2,
  ptr4, (ptr4) are all the same integer
  variable.

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Strings
include ltstdio.hgt main() char msg10 /
array of 10 chars / char p / pointer
to a char / char msg2Hello / msg2
Hello\0 / msg Bonjour /
ERROR. msg has a const address. Think of
space allocation/ p Bonjour / address
of Bonjour goes into p / p msg / OK /
p0 H, p1 i,p2\0 /
p and msg are now Hi Warning be careful if
you have space allocated for p!!/
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Segmentation Fault?

• You reference memory that the OS doesnt want you
  to
• What to check?
• Dereferencing a null pointer 99
• Output or trace with a debugger
• Check array bounds