Custom functions enable C ++ to read CSV files

C ++ is a flexible programming language for applications. We can compile a function suitable for our own development to implement some specific functions based on our own needs. For example, we will introduce a user-defined function to implement the function of reading CSV files in C ++.

• Analysis of concepts related to C ++ static Constructor
• C ++ Traits skills
• Interpretation of c ++ virtual function examples
• What is the relationship between the C ++ function pointer and the C # Delegate?
• The C ++ explicit keyword is applied to the constructor.

Today, we just need a function for C ++ to read CSV files.

No ready-made functions are found, so I wrote one myself.

The objective is to implement C ++ to read CSV files and read each row into an array.

A little unfamiliar, the string processing functions do not know what is ready-made, so they also write two auxiliary string processing functions.

First function: calculate the number of substrings in a string.

 
 

  
  
int strstr_cnt(const char *string, const char 
*substring) {  
  
  
int i,j,k,count = 0;  
  
  
for (i = 0; string[i]; i++){  
  
  
for (j = i, k = 0; (string[j] == 
substring[k] && (j < strlen(string))); j++,k++) {  
  
  
if (! substring[k + 1]) {  
  
  
count++;  
  
  
}  
  
  
}  
  
  
}  
  
  
return count;  
  
  
} 
 
 

Second function: Calculate the position of a substring in the string.

 
 

  
  
int substring_index(const char *s1,const char *s2, int pos){  
  
  
int i,j,k;  
  
  
for( i = pos ; s1[i] ; i++ ) {  
  
  
for( j = i, k = 0 ; s1[j] == s2[k]; j++,k++ ){  
  
  
if (! s2[k + 1]) {  
  
  
return i;  
  
  
}  
  
  
}  
  
  
}  
  
  
return -1;  
  
  
} 
 
 

Function 3: Read a row of a opened CSV file and process the row into an array.

 
 

  
  
char *fgetcsvline(vector<string> &csv_databuf, FILE *fhead) {  
  
  
char *ret_stat;  
  
  
char data_buf[1024];  
  
  
string stringbuf;  
  
  
ret_stat = fgets( data_buf, 1024, fhead );  
  
  
if (ret_stat != NULL) {  
  
  
int len = strstr_cnt(data_buf,"\",\"");  
  
  
if (len > 0){  
  
  
int pos = substring_index(data_buf,"\",\"",0);  
  
  
int startpos = 1;  
  
  
string csv_buf;  
  
  
while (pos > 0) {  
  
  
stringbuf = (string)data_buf;  
  
  
csv_buf = stringbuf.substr(startpos,pos - startpos);  
  
  
csv_databuf.push_back(csv_buf);  
  
  
startpos = pos + 3;  
  
  
pos = substring_index(data_buf,"\",\"",pos + 2);  
  
  
}  
  
  
if ((substring_index(data_buf,"\n",0)) > 0){  
  
  
csv_buf = stringbuf.substr(startpos, stringbuf.length() 
- startpos - 2);  
  
  
} else {  
  
  
csv_buf = stringbuf.substr(startpos, stringbuf.length() 
- startpos - 1);  
  
  
}  
  
  
csv_databuf.push_back(csv_buf);  
  
  
}  
  
  
}  
  
  
return ret_stat;   
  
  
} 
 
 

This function uses the above two functions to process strings.

In addition, the CSV file to be processed by this function is in double quotation marks format:

 
 

  
  
"sss","ddd","444"  
  
  
"ttt","www","ooo"  
  
  
"sss","qqq","000" 
 
 

The usage is as follows:

 
 

  
  
int main(int argc, char* argv[]) {  
  
  
FILE *fp_head;  
  
  
string csvFileName = "test.csv";  
  
  
char *ret_stat;  
  
  
vector<string> csv_data;  
  
  
fp_head = fopen( csvFileName, "rt" );  
  
  
ret_stat = fgetcsvline(csv_data, fp_head);  
  
  
while (ret_stat != NULL) {  
  
  
//get csv data use csv_data[n]  
  
  
ret_stat = fgetcsvline(csv_data, fp_head);  
  
  
}  
  
  
return 0;  
  
  
} 
 
 

The above code may require a little debugging. You can also slightly modify it to read csv files in other formats.

The above is how C ++ reads CSV files.