我将尝试按目前的问题和解决方案进行详细描述。我目前拥有的解决方案不是最优的，我想使其更好。
注意：char inputline[1024]没有特定格式，可以包含任何格式的字符串。char inputline [1024]从具有数千行的文件中逐行读取行。这就是为什么优化对我来说非常重要的原因。
FILE *outfile = fopen("tests.txt", "w");
int start_index = 1; //index from where I want to write the characters from the inputline array to the file
int prev_index = start_index; //keep track of last character position written to file
char inputline[1024] = {"12044 This is the test String 2019 to 2025 is another test& and 2050"};
int loop_count = 6; // This can vary as I have just hardcoded a value here for testing
int i;
for(i=0; i<loop_count; ++i)
{
fprintf(outfile, "%c", inputline[prev_index + i]);
}
prev_index = prev_index + loop_count;// this keeps track of last position of character written to file at end
Sample input in char inputline[1024] = {"This is my day in 2020 1230023"}
Desired output in tests.txt: (for loop will loop 6 times as loop_count is 6)
his is
问题是我正在阅读"%c"，这不是很理想，我想%s改用它。但是我无法理解如何在写入文件时通过指定in格式说明符将其转换为fprintf(outfile, "%c", inputline[prev_index + i]);要使用"%s"的prev_index + i格式，因为我只希望inputline[prev_index + i]基于要写入文件的循环使用来自其中的字符。
您可以使用格式说明符%.*s并传入length
#include <stdio.h>
int main(void) {
int start_index = 1;
int length = 6;
char inputline[] = "This is my day in 2020 1230023";
printf("%.*s\n", length, inputline + start_index); // you can use fprintf(outfile, "%.*s", length, inputline + start_index); here
return 0;
}
输出：
他的是
另外，您可以使用strncpy()创建子字符串并使用它：
#include <stdio.h>
#include <string.h>
int main(void) {
int start_index = 1;
int loop_count = 6;
char inputline[] = "This is my day in 2020 1230023";
char substr[1024];
strncpy ( substr, inputline + start_index, loop_count);
substr[loop_count] = '\0';
printf("%s\n", substr); // you can use fprintf(outfile, "%s", substr); here
return 0;
}
请注意，您必须#include <string.h>在代码中
输出：
他的是
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