2017-07-12-gnu-readline
Table of Contents
1 makefile文件
.PHONY:a.out a.out: cc -g -lreadline hello.c -o hello cc -g -lreadline main.c -o main clean: rm -rfv a.out* *.o
2 Hello,World
#include <stdio.h> #include <stdlib.h> #include <readline/readline.h> #include <readline/history.h> int main() { printf( "%s\n", readline( "test> " ) ); return 0; }
3 防止内存泄露
readline() 返回的字符串是使用 malloc() 分配的，调用者在使用完毕
后，需要使用 free() 来释放内存。不然会泄露。
下面这个代码用 valgrind 扫一下：
#include <stdio.h> #include <stdlib.h> #include <readline/readline.h> #include <readline/history.h> int main() { char *line; line = readline("test> "); printf( "%s\n", line); /* free(line); */ return 0; }
/tmp/readline/ valgrind ./hello
==74398== Memcheck, a memory error detector
==74398== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==74398== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==74398== Command: ./hello
==74398==
test> xiepeng nihao
xiepeng nihao
==74398==
==74398== HEAP SUMMARY:
==74398== in use at exit: 214,423 bytes in 358 blocks
==74398== total heap usage: 496 allocs, 138 frees, 239,503 bytes allocated
==74398==
==74398== LEAK SUMMARY:
==74398== definitely lost: 15 bytes in 1 blocks
==74398== indirectly lost: 0 bytes in 0 blocks
==74398== possibly lost: 2,064 bytes in 1 blocks
==74398== still reachable: 191,796 bytes in 167 blocks
==74398== suppressed: 20,548 bytes in 189 blocks
==74398== Rerun with --leak-check=full to see details of leaked memory
==74398==
==74398== For counts of detected and suppressed errors, rerun with: -v
==74398== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
提示输入的字符串都泄露啦。
把后面的 free() 加上就好了：
#include <stdio.h> #include <stdlib.h> #include <readline/readline.h> #include <readline/history.h> int main() { char *line; line = readline("test> "); printf( "%s\n", line); free(line); return 0; }
/tmp/readline/ valgrind ./hello
==74584== Memcheck, a memory error detector
==74584== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==74584== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==74584== Command: ./hello
==74584==
test> xiepeng nihao
xiepeng nihao
==74584==
==74584== HEAP SUMMARY:
==74584== in use at exit: 214,408 bytes in 357 blocks
==74584== total heap usage: 496 allocs, 139 frees, 239,503 bytes allocated
==74584==
==74584== LEAK SUMMARY:
==74584== definitely lost: 0 bytes in 0 blocks
==74584== indirectly lost: 0 bytes in 0 blocks
==74584== possibly lost: 2,064 bytes in 1 blocks
==74584== still reachable: 191,796 bytes in 167 blocks
==74584== suppressed: 20,548 bytes in 189 blocks
==74584== Rerun with --leak-check=full to see details of leaked memory
==74584==
==74584== For counts of detected and suppressed errors, rerun with: -v
==74584== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
4 basic behavior
#include <stdio.h> #include <stdlib.h> #include <readline/readline.h> #include <readline/history.h> /* A static variable for holding the line. */ static char *line_read = (char *)NULL; /* Read a string, and return a pointer to it. Returns NULL on EOF. */ char* rl_gets () { /* If the buffer has already been allocated, return the memory to the free pool. */ if (line_read) { free (line_read); line_read = (char *)NULL; } /* Get a line from the user. */ line_read = readline (""); /* If the line has any text in it, save it on the history. */ if (line_read && *line_read) add_history (line_read); return (line_read); } int main() { char * line; line = rl_gets(); printf("line = %s\n", line); return 0; }