python stdout.flush（）不刷新最后一个白色字符，如'\n'；
我有两个节目。用C++编写的第一个（python stdout.flush（）不刷新最后一个白色字符，如'\n'；,python,stdout,stdin,flush,Python,Stdout,Stdin,Flush,我有两个节目。用C++编写的第一个（subprocess.cpp）： #include <stdio.h> int main() { char * line = new char[1000]; // first scan scanf("%s\n", line); printf("%s\n", line); fflush(stdout); // second scan scanf("%s\n", line); pr
subprocess.cpp#include <stdio.h>
int main() {
char * line = new char[1000];
// first scan
scanf("%s\n", line);
printf("%s\n", line);
fflush(stdout);
// second scan
scanf("%s\n", line);
printf("%s\n", line);
fflush(stdout);
return 0;
}
marcin@marcin-Aspire-7540 ~/Desktop/inzynierka $ g++ subprocess.cpp -o subprocess
marcin@marcin-Aspire-7540 ~/Desktop/inzynierka $ python test.py
Subprocess line 1 :: abc
test.py子进程的第二行。程序子进程
无法发送第二个字符串，因为它正在等待'\n'字符
pid 6611: test.py
pid 6613: subprocess
> strace -f python test.py
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6613] read(0, "abc\nxyz\n", 4096) = 8
...
[pid 6613] write(1, "abc\n", 4) = 4
[pid 6611] <... read resumed> "a", 1) = 1
[pid 6613] read(0, <unfinished ...>
[pid 6611] read(5, "b", 1) = 1
[pid 6611] read(5, "c", 1) = 1
[pid 6611] read(5, "\n", 1) = 1
...
[pid 6611] write(1, "Subprocess line 1 :: abc\n", 25Subprocess line 1 :: abc) = 25
[pid 6611] write(1, "\n", 1) = 1
[pid 6611] read(5,
如果我将subprocess.cpp
中的第二个scanf
更改为scanf（“%s\n”，行）（不\n
）一切正常。当我在test.py
中再发送一行时也会发生同样的情况：
# send initial data
my_process.stdin.write('abc\n')
my_process.stdin.flush()
my_process.stdin.write('xyz\n')
my_process.stdin.flush()
my_process.stdin.write('ADDITIONAL\n')
my_process.stdin.flush()
Python似乎没有在刷新后发送最后\n个字符（请参见更改了scanf的示例）。在test.py
中添加一个额外的写入和刷新可以证明，在刷新之后，缺少的\n字符仍然在缓冲区中
那怎么办？如何使Python的flush刷新所有字符？错误在于使用i格式字符串的scanf行为。在使用管道时，scanf（“%s\n”）将在\n之后的第一个非空白字符之后返回，或者在使用终端时在第一个非空行之后返回（因为第一个非空白字符将在下一个\n之后刷新）
关键是您可能不是有意使用scanf（“%s\n”）。我猜你真正想要的是：
scanf("%s%*[^\n]", line);
它将读取word，然后丢弃同一行中的所有字符。错误在于\n i格式字符串的扫描行为。在使用管道时，scanf（“%s\n”）将在\n之后的第一个非空白字符之后返回，或者在使用终端时在第一个非空行之后返回（因为第一个非空白字符将在下一个\n之后刷新）
关键是您可能不是有意使用scanf（“%s\n”）。我猜你真正想要的是：
scanf("%s%*[^\n]", line);
它将读取单词，然后丢弃同一行中的所有字符。问题在于scanf（“%s\n”，line）
，第二个scanf（）
需要读取另一行才能找到非空白字符
pid 6611: test.py
pid 6613: subprocess
> strace -f python test.py
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6613] read(0, "abc\nxyz\n", 4096) = 8
...
[pid 6613] write(1, "abc\n", 4) = 4
[pid 6611] <... read resumed> "a", 1) = 1
[pid 6613] read(0, <unfinished ...>
[pid 6611] read(5, "b", 1) = 1
[pid 6611] read(5, "c", 1) = 1
[pid 6611] read(5, "\n", 1) = 1
...
[pid 6611] write(1, "Subprocess line 1 :: abc\n", 25Subprocess line 1 :: abc) = 25
[pid 6611] write(1, "\n", 1) = 1
[pid 6611] read(5,
类似的情况有很好的解释
我还用strace
检查了它，Python发送最后一个'\n'
字符
pid 6611: test.py
pid 6613: subprocess
> strace -f python test.py
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6613] read(0, "abc\nxyz\n", 4096) = 8
...
[pid 6613] write(1, "abc\n", 4) = 4
[pid 6611] <... read resumed> "a", 1) = 1
[pid 6613] read(0, <unfinished ...>
[pid 6611] read(5, "b", 1) = 1
[pid 6611] read(5, "c", 1) = 1
[pid 6611] read(5, "\n", 1) = 1
...
[pid 6611] write(1, "Subprocess line 1 :: abc\n", 25Subprocess line 1 :: abc) = 25
[pid 6611] write(1, "\n", 1) = 1
[pid 6611] read(5,
pid 6611:test.py
pid 6613：子流程
>strace-f python test.py
[pid 6611]写入（4，“abc\n”，4
...
[pid 6611]写入（4，“abc\n”，4
...
[pid 6613]读取（0，“abc\nxyz\n”，4096）=8
...
[pid 6613]写入（1，“abc\n”，4）=4
[pid 6611]“a”，1）=1
[pid 6613]读取（0，
[pid 6611]读取（5，“b”，1）=1
[pid 6611]读取（5，“c”，1）=1
[pid 6611]读取（5，“\n”，1）=1
...
[pid 6611]写入（1，“子流程行1:：abc\n”，25子流程行1:：abc）=25
[pid 6611]写入（1，“\n”，1）=1
[pid 6611]读取（5，
问题在于scanf（“%s\n”，line）
，第二个scanf（）
需要读取另一行才能找到非空白字符
pid 6611: test.py
pid 6613: subprocess
> strace -f python test.py
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6613] read(0, "abc\nxyz\n", 4096) = 8
...
[pid 6613] write(1, "abc\n", 4) = 4
[pid 6611] <... read resumed> "a", 1) = 1
[pid 6613] read(0, <unfinished ...>
[pid 6611] read(5, "b", 1) = 1
[pid 6611] read(5, "c", 1) = 1
[pid 6611] read(5, "\n", 1) = 1
...
[pid 6611] write(1, "Subprocess line 1 :: abc\n", 25Subprocess line 1 :: abc) = 25
[pid 6611] write(1, "\n", 1) = 1
[pid 6611] read(5,
类似的情况有很好的解释
我还用strace
检查了它，Python发送最后一个'\n'
字符
pid 6611: test.py
pid 6613: subprocess
> strace -f python test.py
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6611] write(4, "abc\n", 4 <unfinished ...>
...
[pid 6613] read(0, "abc\nxyz\n", 4096) = 8
...
[pid 6613] write(1, "abc\n", 4) = 4
[pid 6611] <... read resumed> "a", 1) = 1
[pid 6613] read(0, <unfinished ...>
[pid 6611] read(5, "b", 1) = 1
[pid 6611] read(5, "c", 1) = 1
[pid 6611] read(5, "\n", 1) = 1
...
[pid 6611] write(1, "Subprocess line 1 :: abc\n", 25Subprocess line 1 :: abc) = 25
[pid 6611] write(1, "\n", 1) = 1
[pid 6611] read(5,
pid 6611:test.py
pid 6613：子流程
>strace-f python test.py
[pid 6611]写入（4，“abc\n”，4
...
[pid 6611]写入（4，“abc\n”，4
...
[pid 6613]读取（0，“abc\nxyz\n”，4096）=8
...
[pid 6613]写入（1，“abc\n”，4）=4
[pid 6611]“a”，1）=1
[pid 6613]读取（0，
[pid 6611]读取（5，“b”，1）=1
[pid 6611]读取（5，“c”，1）=1
[pid 6611]读取（5，“\n”，1）=1
...
[pid 6611]写入（1，“子流程行1:：abc\n”，25子流程行1:：abc）=25
[pid 6611]写入（1，“\n”，1）=1
[pid 6611]读取（5，
scanf（“%s”，line）get（line）scanf（“%s”，line）获取（line）