調試時GDB printf奇怪的輸出

爲什麼printf的輸出在出線時不顯示？但在某些時候它沒有印刷生產線16調試時GDB printf奇怪的輸出

C文件：

#include<stdio.h> 

void nextfunc(){ 
    int ctr;  
    for(ctr = 0; ctr<3; ctr++){ 
     printf("print ctr = %d",ctr); 
    } 
    printf("last print"); 
} 
void main(){ 

    int x; 
    printf("input x: "); 
    scanf("%d",&x); 
    printf("\nprint 2"); 
    printf("\nprint 3"); 
    nextfunc(); 
}

GDB：

(gdb) break main 
    Breakpoint 1 at 0x8048479: file file5.c, line 14. 
    (gdb) break nextfunc 
    Breakpoint 2 at 0x804843a: file file5.c, line 6. 
    (gdb) run 
    Starting program: /home/charmae/workspace/AVT/file5 

    Breakpoint 1, main() at file5.c:14 
    14  printf("input x: "); 
    (gdb) s 
    15  scanf("%d",&x); 
    (gdb) s 
    input x: 4 
    16  printf("\nprint 2"); 
    (gdb) s 

    17  printf("\nprint 3"); 
    (gdb) s 
    print 2 
    18  nextfunc(); 
    (gdb) s 

    Breakpoint 2, nextfunc() at file5.c:6 
    6  for(ctr = 0; ctr<3; ctr++){ 
    (gdb) s 
    7   printf("print ctr = %d",ctr); 
    (gdb) s 
    6  for(ctr = 0; ctr<3; ctr++){ 
    (gdb) s 
    7   printf("print ctr = %d",ctr); 
    (gdb) s 
    6  for(ctr = 0; ctr<3; ctr++){ 
    (gdb) s 
    7   printf("print ctr = %d",ctr); 
    (gdb) s 
    6  for(ctr = 0; ctr<3; ctr++){ 
    (gdb) s 
    9  printf("last print"); 
    (gdb) s 
    10 } 
    (gdb) s 
    main() at file5.c:19 
    19 } 
    (gdb) s 
    0x0014a113 in __libc_start_main() from /lib/i386-linux-gnu/libc.so.6 
    (gdb) s 
    Single stepping until exit from function __libc_start_main, 
    which has no line number information. 
    print 3print ctr = 0print ctr = 1print ctr = 2last print[Inferior 1 (process 2578) exited with code 012]

來源

2011-11-23 Chinwei