What does int argc char argv mean

Question

In many C   IDE s and compilers  when it generates the main function for you  it looks like this   int main int argc  char  argv      When I code C   without an IDE  just with a command line compiler  I type   int main     without any parameters   What does this mean  and is it vital to my program

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argv and argc are how command line arguments are passed to main   in C and C     argc will be the number of strings pointed to by argv   This will  in practice  be 1 plus the number of arguments  as virtually all implementations will prepend the name of the program to the array   The variables are named argc  argument count  and argv  argument vector  by convention  but they can be given any valid identifier  int main int num args  char   arg strings  is equally valid   They can also be omitted entirely  yielding int main    if you do not intend to process command line arguments   Try the following program    include  lt iostream gt   int main int argc  char   argv        std  cout  lt  lt   Have    lt  lt  argc  lt  lt    arguments    lt  lt  std  endl      for  int i   0  i  lt  argc    i            std  cout  lt  lt  argv i   lt  lt  std  endl            Running it with   test a1 b2 c3 will output  Have 4 arguments    test a1 b2 c3

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int main      This is a simple declaration  It cannot take any command line arguments   int main int argc  char  argv       This declaration is used when your program must take command-line arguments  When run like such   myprogram arg1 arg2 arg3   argc  or Argument Count  will be set to 4  four arguments   and argv  or Argument Vectors  will be populated with string pointers to  myprogram    arg1    arg2   and  arg3   The program invocation  myprogram  is included in the arguments   Alternatively  you could use   int main int argc  char   argv     This is also valid   There is another parameter you can add   int main  int argc  char  argv    char  envp      The envp parameter also contains environment variables  Each entry follows this format   VARIABLENAME VariableValue   like this   SHELL  bin bash       The environment variables list is null-terminated   IMPORTANT  DO NOT use any argv or envp values directly in calls to system    This is a huge security hole as malicious users could set environment variables to command-line commands and  potentially  cause massive damage  In general  just don t use system    There is almost always a better solution implemented through C libraries

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The main function can have two parameters  argc and argv  argc is an integer  int  parameter  and it is the number of arguments passed to the program    The program name is always the first argument  so there will be at least one argument to a program and the minimum value of argc will be one  But if a program has itself two arguments the value of argc will be three    Parameter argv points to a string array and is called the argument vector  It is a one dimensional string array of function arguments

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argc is the number of arguments being passed into your program from the command line and argv is the array of arguments   You can loop through the arguments knowing the number of them like   for int i   0  i  lt  argc  i             argv i  is the argument at index i

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Both of  int main int argc  char  argv     int main      are legal definitions of the entry point for a C or C   program  Stroustrup  C   Style and Technique FAQ details some of the variations that are possible or legal for your main function

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The parameters to main represent the command line parameters provided to the program when it was started  The argc parameter represents the number of command line arguments  and char  argv   is an array of strings  character pointers  representing the individual arguments provided on the command line

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Suppose you run your program thus  using sh syntax     myprog arg1 arg2  arg 3    If you declared your main as int main int argc  char  argv     then  in most environments   your main   will be called as if like   p      myprog    arg1    arg2    arg 3   NULL    exit main 4  p      However  if you declared your main as int main    it will be called something like  exit main       and you don t get the arguments passed   Two additional things to note    These are the only two standard-mandated signatures for main   If a particular platform accepts extra arguments or a different return type  then that s an extension and should not be relied upon in a portable program   argv   and   argv are exactly equivalent  so you can write int main int argc  char  argv    as int main int argc  char   argv

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The first parameter is the number of arguments provided and the second parameter is a list of strings representing those arguments

[c++] What does int argc, char *argv[] mean?

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