How do I set a conditional breakpoint in gdb when char x points to a string whose value equals hello

Question

Can I specify that I want gdb to break at line x when char  x points to a string whose value equals  hello   If yes  how

User · Answer

break x if   int strcmp y   hello       0   On some implementations gdb might not know the return type of strcmp  That means you would have to cast  otherwise it would always evaluate to true

User · Answer

Since GDB 7 5 you can use these native Convenience Functions    memeq buf1  buf2  length    regex str  regex    streq str1  str2    strlen str   Seems quite less problematic than having to execute a  quot foreign quot  strcmp   on the process  stack each time the breakpoint is hit  This is especially true for debugging multithreaded processes   Note your GDB needs to be compiled with Python support  which is not an issue with current linux distros  To be sure  you can check it by running show configuration inside GDB and searching for --with-python  This little oneliner does the trick  too    gdb -n -quiet -batch -ex  show configuration    grep  with-python               --with-python  usr  relocatable    For your demo case  the usage would be  break  lt where gt  if   streq x   quot hello quot    or  if your breakpoint already exists and you just want to add the condition to it condition  lt breakpoint number gt    streq x   quot hello quot      streq only matches the whole string  so if you want something more cunning you should use   regex  which supports the Python regular expression syntax

User · Answer

You can use strcmp   break x 20 if strcmp y   hello      0   20 is line number  x can be any filename and y can be any variable

[c] How do I set a conditional breakpoint in gdb, when char* x points to a string whose value equals "hello"?

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