[英]Match two strings with = as separator in fscanf
My aim is to extract the value and a key separated by an =
. 我的目的是提取值和由=
分隔的键。 My initial idea was to use something like %s=%s
, but unfortunately it doesn't work. 我最初的想法是使用%s=%s
类%s=%s
东西,但是不幸的是它不起作用。
So I have a file: 所以我有一个文件:
A=1
B=2
So I open the file: 所以我打开文件:
char *key;
char *value;
FILE* file = fopen("./file", "r");
do {
fscanf(file, "%[^'=']=%[^'\n']\n", key, value);
printf("key:%s value:%s\n", key, value);
} while(!feof(file));
However both key and value return: 但是键和值都返回:
key:1 value:1
key:2 value:2
Any idea why my expression is not matching?. 知道我的表情为什么不匹配吗?
key
and value
variables must be allocated, eg 必须分配key
和value
变量,例如
char key[100];
char value[1000];
Then use them. 然后使用它们。
char key[16];//char *key;//not point to memory for store.
char value[16];
FILE *file = fopen("./file", "r");
while(2==fscanf(file, " %[^=]=%[^\n]", key, value)){
printf ("key:%s value:%s\n", key, value);
}
Your pointers are uninitialized. 您的指针未初始化。 Reading them is undefined in C. You can use arrays (if you know the maximal lengths at compile-time) or allocate memory with malloc
. 读取它们在C中是未定义的。您可以使用数组(如果知道编译时的最大长度)或使用malloc
分配内存。
Read the *scanf
documentation carefully, these functions are a little tricky. 仔细阅读*scanf
文档,这些功能有些棘手。
"%s=%s"
cannot match, %s
consumes all =
signs so the following =
is always a matching failure (the next character after %s
is always a whitespace or EOF). "%s=%s"
无法匹配, %s
消耗了所有=
符号,因此以下=
始终是匹配失败( %s
之后的下一个字符始终是空格或EOF)。
When reading strings, always use a maximum field width (in some cases, it can be omitted safely, but only for sscanf
). 读取字符串时,请始终使用最大字段宽度(在某些情况下,可以安全地将其省略,但仅适用于sscanf
)。 Unfortunately, you have to hard-code that value (or build up the format string at run-time, but I wouldn't advise you to do so). 不幸的是,您必须对该值进行硬编码(或在运行时构建格式字符串,但我不建议您这样做)。
I'm not sure what the '
in the scan sets are supposed to do, %[^'=']
is equivalent to %[^'=]
and matches everything but '
and =
. 我不确定扫描集中的'
应该做什么, %[^'=']
等同于%[^'=]
并匹配'
和=
所有内容。 You've probably meant %[^=]
. 您可能是说%[^=]
。
Every white-space character in the format string (outside a scan set) is treated equally as "skip any white-space", that is, a space ( 格式字符串中(扫描集之外)的每个空格字符均被视为“跳过任何空格”,即空格( ) is the same as a newline. )与换行符相同。 The whole format string is equivalent to 整个格式字符串等效于
"%[^'=]=%[^'\n] " // Note the space at the end
To match a literal newline, you need to use a scanset (with a length). 要匹配文字换行符,您需要使用扫描集(具有长度)。
Always check the return value of *scanf
(also for fopen
and any other function which can fail). 始终检查*scanf
的返回值(也用于fopen
和任何其他可能失败的函数)。
char key[64]; // Or whatever is appropriate for you,
char value[64]; // remember the 0-terminator needs one byte
FILE *file = fopen("./file", "r");
if(!file) {
perror("./file");
exit(1);
}
for(;;) {
int e = fscanf(file, "%63[^=]=%63[^\n]%1[\n]", key, value, (char[2]){ 0 });
if(e == -1) {
if(ferror(file)) {
perror("reading from ./file");
// handle read error
} else { // EOF reached on first character of line
break;
}
} else if(e < 3) {
// handle invalid input
} else {
printf("key:%s value:%s\n", key, value);
}
}
Alternatively, you could use assignment-suppression for the last newline as in "%63[^=]=%63[^\\n]%*1[\\n]"
and omit the last argument to fscanf
. 或者,您可以对最后一个换行符使用赋值抑制,如"%63[^=]=%63[^\\n]%*1[\\n]"
并省略fscanf
的最后一个参数。 By doing so, you can no longer detect if the last line ended in a newline. 这样,您将无法再检测最后一行是否以换行符结尾。
My initial idea was to use something like
%s=%s
, but unfortunately it doesn't work. 我最初的想法是使用%s=%s
类%s=%s
东西,但是不幸的是它不起作用。
Thats simply because *scanf
does not respect non-whitespace delimiters as you suspected. 那仅仅是因为*scanf
不像您怀疑的那样尊重非空白定界符。 Furthermore, it does not support real regular expressions. 此外,它不支持真正的正则表达式。 Only a certain simple type of character classes [..]
are supported. 仅支持某些简单类型的字符类[..]
。
To your problem: 给你的问题:
key
and value
have to be allocated static or dynamic, the rest can be simplified and written without fscanf
(your input is obviously line-oriented), which might get you into trouble at some point : key
和value
必须静态或动态分配,其余的可以简化和编写而无需fscanf
(您的输入显然是面向行的),这可能会在某些时候给您带来麻烦 :
...
FILE* fh = fopen("file", "r");
char buffer[1024]; /* line buffer for reading file if file is line-oriented */
while( fgets(buffer, sizeof(buffer), fh) ) {
char key[256], val[256];
sscanf(buffer, "%[^=]=%[^\n]", key, val);
printf("key:%s val:%s\n", key, val);
}
fclose(fh);
...
Edit the length of the scan buffers ( key[256]
, val[256]
) depending on your input. 根据您的输入,编辑扫描缓冲区的长度( key[256]
, val[256]
)。
// sample working code
#include<stdio.h>
#include<stdlib.h>
int main(void) {
FILE* file = fopen("./file", "r");
if(NULL == file) {
printf("Failed to open file\n");
return EXIT_FAILURE;
}
do {
char key[256];
char value[256];
fscanf(file, "%[^'=']=%[^'\n']\n", key, value);
printf("key:%s value:%s\n", key, value);
}while(!feof(file));
fclose(file);
return EXIT_SUCCESS;
} // End of main()
Sample Output: 样本输出:
key:A value:1
key:B value:2
key:C value:3
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