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This article mainly explains "C language how to read a file to find the average of a column", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Now let the editor to take you to learn "C language how to read a file to find the average of a certain column"!

Part one: compare the efficiency of reading files

First, randomly generate a file with 10 million lines and 4 columns (which will be used below). Let's take a look at the efficiency of the above functions in reading files:

As can be seen from the above figure, fread is the most efficient and fgetc is the least efficient. Of course, this comparison is very superficial, but you can roughly see the trend.

The code for each function to read the file is as follows: the main function is the same, but the implementation of the readFile function is different.

# include # define BUFSIZE 4096 void readFile (FILE* fp); int main (int argc, char* argv []) {FILE* fp; time_t start, end; start = time (NULL); if (argc)

< 2) { printf("Usage: %s \n", argv[0]); return 1; } if ((fp = fopen(argv[1], "r")) == NULL) { printf("Error: cannot open file\n"); return 1; } readFile(fp); fclose(fp); end = time(NULL); printf("time spent: %d seconds\n", end - start); return 0; } // readFile_fgetc: void readFile(FILE* fp) { char c; while ((c = fgetc(fp)) != EOF) ; } // readFile_fgets: void readFile(FILE* fp) { char buf[BUFSIZE]; while (fgets(buf, MAXLINE, fp) != NULL) ; } // readFile_fread: void readFile(FILE* fp) { char buf[BUFSIZE]; while (fread(buf, 1, BUFSIZE, fp) >

0);} / / readFile_fscanf: void readFile (FILE* fp) {char buf [BUFSIZE]; while (fscanf (fp, "% [^\ n] s", buf) = = 1);} part 2: compare the efficiency of finding column averages

So how efficient is it for each function to calculate the column average? We still use the above 10 million-line file and use the above functions to calculate the average of the second column, and their efficiency is as follows:

The code is as follows: the main function is roughly the same, but the implementation of the colAver function is different.

This code handles EOF perfectly, running correctly regardless of whether the file ends with a blank line or not. However, there is still the premise that the delimiter (number of columns) of each line in the file is the same, otherwise the code may go wrong. )

Of these codes, fscanf is the shortest, and this function can greatly improve the programming efficiency of formatting reading data.

# include # define BUFSIZE 4096void getColAver (FILE* fp, const int k); int main (int argc, char* argv []) {FILE* fp; time_t start, end; start = time (NULL); if (argc

< 2) { printf("Usage: %s \n", argv[0]); return 1; } if ((fp = fopen(argv[1], "r")) == NULL) { printf("Error: cannot open file\n"); return 1; } getColAver(fp, 2); fclose(fp); end = time(NULL); printf("time spent: %d seconds\n", end - start); return 0; } // colAver_fgetc: void getColAver(FILE* fp, const int k) { int i = 0; // num of '\t' int j = 0; // num of chars int c; // char char col[50]; float sum = 0; int n = 0; // num of lines. int inCol = 0; while ((c = fgetc(fp)) != EOF) { if (i == k - 1) { inCol = 1; if (c == '\t') i++; else if (c == '\n') i = 0; else col[j++] = c; } else { if (c == '\t') i++; else if (c == '\n') i = 0; if (inCol) { col[j] = '\0'; sum += atof(col); n++; } j = 0; inCol = 0; } } if (inCol) { col[j] = '\0'; sum += atof(col); n++; } if (n == 0) printf("Error: no line!\n"); else printf("The average of col %d is %f\n", k, sum / n); } // colAver_fgets: void getColAver(FILE* fp, const int k) { int i = 0; // num of '\t' int j = 0; // num of chars char col[50]; char buf[BUFSIZE]; float sum = 0; int n = 0; // num of lines. int inCol = 0; char* p; while (fgets(buf, BUFSIZE, fp) != NULL) { for (p = buf; *p != '\0'; p++) { if (i == k - 1) { inCol = 1; if (*p == '\t') i++; else if (*p == '\n') i = 0; else col[j++] = *p; } else { if (*p == '\t') i++; else if (*p == '\n') i = 0; if (inCol) { col[j] = '\0'; sum += atof(col); n++; } j = 0; inCol = 0; } } } if (inCol) { col[j] = '\0'; sum += atof(col); n++; } if (n == 0) printf("Error: no line!\n"); else printf("The average of col %d is %f\n", k, sum / n); } // colAver_fread: void getColAver(FILE* fp, const int k) { int i = 0; // num of '\t' int j = 0; // num of chars char col[50]; char buf[BUFSIZE]; float sum = 0; int n = 0; // num of lines. int m, l; int sizeChr = sizeof(char); int inCol = 0; while ((l = fread(buf, sizeChr, BUFSIZE, fp)) >

0) {for (m = 0; m < 1; mcm +) {if (I = = k-1) {inCol = 1; if (buf [m] = ='\ t') iTunes; else if (buf [m] = ='\ n') I = 0; else col [jacks +] = buf [m];} else {if (buf [m] = ='\ t') imanagers + Else if (buf [m] = ='\ n') I = 0; if (inCol) {col [j] ='\ 0mm; sum + = atof (col); inCol = 0; inCol = 0;} if (inCol) {col [j] ='\ 0mm; sum + = atof (col); nasty + } if (n = 0) printf ("Error: no line!\ n"); else printf ("The average of col% d is% f\ n", k, sum / n);} / / colAver_fscanf: void getColAver (FILE* fp) {float f; float sum = 0; int n = 0; / / num of lines. While (fscanf (fp, "% * s% f% * [^\ n] s", & f) = = 1) {sum + = f; n = 0) printf ("Error: no line!\ n"); else printf ("The average of col 2 is% f\ n", sum / n) } at this point, I believe you have a deeper understanding of "C language how to read files to find the average of a column". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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