here<\/a>.<\/p>\nCompile that code using:
\ngcc -o strcmp -g strcmp.c<\/p>\n
Fire up the debugger using:
\ngdb strcmp<\/p>\n
You’ll get the gdb prompt:
\n(gdb)<\/p>\n
Set a break point at the start:
\nb main<\/p>\n
The debugger will echo something like:
\nBreakpoint 1 at 0x80483d5: file strcmp.c, line 6.
\n(gdb) <\/p>\n
Then run the program:
\nrun<\/p>\n
The debugger will print out something like:
\nStarting program: \/home\/somedude\/bin\/strcmp <\/p>\n
Breakpoint 1, main () at strcmp.c:6
\n6\t{
\n(gdb) <\/p>\n
If you type n a few times, you’ll eventually get to some variable assignments.<\/p>\n
\r\n(gdb) n\r\n8\tchar s1[] = \"better\";\r\n(gdb) n\r\n9\tchar s2[] = \"better than\"; \/* than this\";*\/\r\n(gdb) n\r\n11\tint i_result = 0;\r\n(gdb) n\r\n13\ti_result = bstrcmp(s1,s2);\r\n<\/pre>\nIf you want to the values of these variables type:
\np i_result<\/p>\n
You get back:
\n(gdb) p i_result
\n$1 = 0<\/p>\n
To step into a function, type s:<\/p>\n
\r\n(gdb) s\r\nbstrcmp (s1=0xbf86b469 \"better\", s2=0xbf86b474 \"better than\") at strcmp.c:26\r\n26\t\twhile(*s1 == *s2++) { \r\n(gdb) n\r\n27\t\t\tif(*s1++ == 0){ return 0; } \r\n(gdb) n\r\n26\t\twhile(*s1 == *s2++) { \r\n(gdb) n\r\n27\t\t\tif(*s1++ == 0){ return 0; } \r\n(gdb) n\r\n26\t\twhile(*s1 == *s2++) { \r\n(gdb) \r\n<\/pre>\nAt this point you can type things like:
\np s1
\np *s1
\np s2
\np *s2<\/p>\n
And you’ll get back the value of the pointers and what’s in memory.<\/p>\n
Next time we’ll go over how to do this with PHP running single threaded on debug mode on Apache.<\/p>\n","protected":false},"excerpt":{"rendered":"
Here’s a pretty compact version of strcmp: int bstrcmp(char *s1,char *s2) { while(*s1 == *s2++) { if(*s1++ == 0){ return 0; } } return (*(unsigned char *)s1 – *(unsigned char*)–s2); } The source that I used for compiling and calling this version of strcmp is here. Compile that code using: gcc -o strcmp -g strcmp.c […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,1],"tags":[90,76,100,99,98],"class_list":["post-72","post","type-post","status-publish","format-standard","hentry","category-how-to","category-uncategorized","tag-c","tag-coding","tag-debugging","tag-gcc","tag-gdb"],"_links":{"self":[{"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/posts\/72","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/comments?post=72"}],"version-history":[{"count":0,"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/posts\/72\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/media?parent=72"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/categories?post=72"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.codebelay.com\/blog\/wp-json\/wp\/v2\/tags?post=72"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}